<p>This plugin will scan your thumbnail-less posts and look for a suitable image to use as a thumbnail.<br />
It will look for images linked in the post content and will download and add them to the local library.<br />
Post scanning is performed only when <code>the_post_thumbnail</code> or <code>get_the_post_thumbnail</code> are called for<br />
that particular post.</p>
<p>So you designed your new thumbnail-based template, but you have tons of thumbnail-less posts and<br />
don’t want to spend too much time on scraping your old posts for a thumbnail picture. Maybe you<br />
think you will probably forget to set a thumbnail for your new posts. Maybe both, as was my case :).</p>
<p>When a thumbnail for a post is queried and nothing is found this plugin will scrape the post for<br />
an <code><img></code> tag and its <code>href</code> property. Once a suitabile image is found (based on the configured<br />
settings), it will be downloaded ad set as the post thumbnail. If no suitable image is found,<br />
a default one will be used.</p>
<p>This plugin is still in early development state. It just covers my needs (see the “To do” section<br />
for more details). It has been tested only with wordpress 3.0.1, but should work also with 2.9,<br />
since I used similar code with 2.9 (even if it was included in my template’s <code>functions.php</code>).</p>
<p>The plugin is not supported. This doesn’t mean that I will not look into submitted bugs. Anyway,<br />
don’t expect prompt answers, since this is done in my spare time.</p>
<h3>To do</h3>
<p>Many things should be done in future releases. Here are some:</p>
<ul>
<li>Current version always downloads selected linked images. This works good with images hosted on external sites.<br />
If your posts link to images hosted in your media library, you will end up with two images.</li>
<li>A more user friendly name should be used for images added to the library (e.g. Thumbnail for post …)</li>
<li>Somewhere, a button to reset the “previously scanned” status of all posts should be provided (on current version,<br />
you cas set or reset it for single posts in the edit page.</li>
<li>“previously scanned” status should probably be reset (or at least you should be asked to) when publishing a<br />
updating an existing post</li>
</ul>
<p>More ideas are wellcome.</p>


Automatic Thumbnail Generator

Automated on-demand generation of posts thumbnails.

Mizuho Ogino

<p>By uploading a PDF attachment, this plugin convert the cover page to jpeg and attach it as a post thumbnail file. It also allows displaying a thumbnail icon and inserting PDF link with a cover image into the editor.</p>
<h4>Available only for WordPress 4.0+, also only on the server which  ImageMagick and GhostScript are installed.</h4>
<p>This plugin hooks to the media editor and generates the first page image of PDF by using ImageMagick with GhostScript. It requires no setup, just activate the plugin via the admin install page. Allow to set a PDF as an image.</p>
<h4>How it works</h4>
<p>This Plugin replaces and extends the following features.</p>
<ul>
<li>Generate cover image of PDF by using ImageMagick. Generated Image has different size variations and is attached to PDF.</li>
<li>Register Generated Image as Featured Image (post-thumbnail) of PDF.</li>
<li>Display Generated Image as icon instead of Mime-type Icon in Admin Page.</li>
<li>Hide Generated Image file itself in Media Library. (v1.2 or later)</li>
<li>Replace link text with JPG when inserting PDF to Text Editor.</li>
<li>Delete Generated Image when deleting PDF from Media Library.</li>
<li>Allow to manage and output Generated Image and PDF on manually in template file. (see Other Notes.)</li>
<li>Allow to set PDF as Featured Image and to use functions in the same way as image file. (v1.2 or later, see Other Notes.)</li>
<li>Allow to control maximum size of Generated Image and other default settings in Plugin Page. (v1.3.4 or later)</li>
</ul>
<h4>Generated Items</h4>
<p>A generated image file is registered as post children of a PDF file and it has different size variations. Files build a tree like below.</p>
<ul>
<li>my-file.pdf (Your PDF)
<ul>
<li>my-file-pdf.jpg (Generated Cover Image of Your PDF)
<ul>
<li>my-file-pdf-1024×768.jpg (Large Size)</li>
<li>my-file-pdf-300×225.jpg (Medium Size)</li>
<li>my-file-pdf-150×150.jpg (Thumbnail size)</li>
<li>…(And Your Custom File Sizes)</li>
</ul>
</li>
</ul>
</li>
</ul>
<h4>Insert HTML into the editor</h4>
<p>Select a PDF file in the Media Uploader and insert it into the the editor. An output HTML is automatically rewritten like below.</p>
<pre><code><a class="link-to-pdf" title="dummy-pdf" href="http://exmaple.com/wp-content/uploads/2015/01/dummy-pdf.pdf" target="_blank"><img width="227" height="320" class="size-medium wp-image-9999 thumb-of-pdf" src="http://exmaple.com/wp-content/uploads/2015/01/dummy-pdf-pdf-227x320.jpg" alt="thumbnail-of-dummy-pdf" /></a>
</code></pre>
<p>*If you are using a document viewer plugin (like GDE) and want insert html which is made by it, select “Default (Title)” of “media” selector.</p>
<h4>Get thumbnail in template file</h4>
<p>A generated image ID is stored in [‘_thumbnail_id’] custom field of a PDF attachment post. An image ID is exportable by using get_post_thumbnail_id($your_pdf_id) or get_post_meta($your_pdf_id, ‘_thumbnail_id’, true) functions in a template file.</p>
<pre><code>$pdf_id = 'your PDF file ID';
if ( $thumbnail_id = get_post_thumbnail_id( $pdf_id ) ) {
echo '<a class="pdf-link image-link" href="'.wp_get_attachment_url( $pdf_id ).'" title="'.esc_attr( get_the_title( $pdf_id ) ).'" target="_blank">'.wp_get_attachment_image ( $thumbnail_id, 'medium' ).'</a>';
}
</code></pre>
<p>Or more simply, you can call images and link to PDF files by wp_get_attachment_image($your_pdf_id, $size) and wp_get_attachment_link($your_pdf_id, $size) functions. (v1.2 or later) *If the plugin is deactivated, this function just will return empty.</p>
<pre><code>$pdf_id = 'your PDF file ID';
echo wp_get_attachment_image ( $pdf_id, 'medium' );
echo wp_get_attachment_link ( $pdf_id, 'medium' );
</code></pre>
<p>If you call all PDFs that are attached to the post. You can get them by get_posts function.</p>
<p>Examples.<br />
Dynamically get PDFs that are attached to the post.</p>
<pre><code><?php
$pdfs = get_posts( 'posts_per_page=-1&post_type=attachment&post_mime_type=application/pdf&post_parent='.$post->ID );
if( $pdfs ): foreach( $pdfs as $pdf ):
  $thumbnail_id = get_post_thumbnail_id( $pdf->ID );
  if( $thumbnail_id ):
    echo '<li>';
    echo '<a href="'wp_get_attachment_url( $pdf->ID )'" class="link-to-pdf">';
    echo wp_get_attachment_image ( $thumbnail_id, 'medium' );
    echo '</a>';
    echo '</li>';
  endif;
endforeach; endif;
?>
</code></pre>
<h4>Set PDF thumbnail as Featured Image</h4>
<p>The plugin support you to set PDF as Featured Image. (v1.2 or later)<br />
Strictly explaining, when you set a PDF as Featured Image, the plugin automatically set the thumbnail which is registered with this PDF.<br />
You can call thumbnail by using get_the_post_thumbnail function.</p>
<pre><code>echo get_the_post_thumbnail ( $post->ID, 'medium' );
</code></pre>
<p>May you want pdf file from the post thumbnail.</p>
<pre><code>$thumb_id = get_post_thumbnail_id ( $post->ID );
$pdf_id = get_post( $thumb_id )->post_parent;
if ( $pdf_id && get_post_mime_type ( $pdf_id ) === 'application/pdf' ){
  $pdf = get_post($pdf_id);
  echo '<a class="link-to-pdf" href="'.wp_get_attachment_url($pdf_id).'" title="'.esc_html($pdf->post_title).'" target="_blank">'.get_the_post_thumbnail().'</a>'."\n";
}
</code></pre>
<h4>Display attachment data with in caption</h4>
<p>The plugin allows you to insert [caption] short-code into the post content area as when insert an image. If you want to display attachment title, description, file type, file size and so on, use img_caption_shortcode filter in your functions.php.<br />
Here’s an example code…<br />
    function add_attachment_data_in_caption( $empty, $attr, $content ) {<br />
        $attr = shortcode_atts( array( ‘id’=>”, ‘align’=>’alignnone’, ‘width’=>”, ‘caption’=>” ), $attr );<br />
        if ( 1 > (int) $attr[‘width’] || empty( $attr[‘caption’] ) ) return ”;<br />
        if ( $attr[‘id’] ) {<br />
            $attr[‘id’] = ‘id=”‘ . esc_attr( $attr[‘id’] ) . ‘” ‘;<br />
            $attachment_id = explode(‘_’, $attr[‘id’]);<br />
            $attachment_id = $attachment_id[1];// get attachment id<br />
            if( get_post_mime_type ( $attachment_id ) === ‘application/pdf’ ){<br />
                $attachment = get_post( $attachment_id );<br />
                $bytes = filesize( get_attached_file( $attachment->ID ) );<br />
                if ($bytes >= 1073741824) $bytes = number_format($bytes / 1073741824, 2). ‘ GB’;<br />
                elseif ($bytes >= 1048576) $bytes = number_format($bytes / 1048576, 2). ‘ MB’;<br />
                elseif ($bytes >= 1024) $bytes = number_format($bytes / 1024, 2). ‘ KB’;<br />
                elseif ($bytes > 1) $bytes = $bytes. ‘ bytes’;<br />
                elseif ($bytes == 1) $bytes = $bytes. ‘ byte’;<br />
                else $bytes = ‘0 bytes’;<br />
                $attr[‘caption’] =<br />
                  ‘title : ‘ .$attachment->post_title. ‘<br />‘ . // title<br />
                  ‘caption : ‘ .$attr[‘caption’]. ‘<br />‘ .// caption<br />
                  ‘size : ‘ .$bytes. ‘<br />‘ . // file size<br />
                  ‘filetype : ‘ .get_post_mime_type ( $attachment_id ). ‘<br />‘ . // file type<br />
                  ‘description : ‘ .$attachment->post_content. ‘<br />‘; // description<br />
            }<br />
        }</p>
<pre><code>    return 
      '<div ' .$attr['id']. 'class="wp-caption ' .esc_attr( $attr['align'] ). '" style="max-width: ' .( 10 + (int) $attr['width'] ). 'px;">' .
      do_shortcode( $content ). '<p class="wp-caption-text">' .$attr['caption']. '</p>' .
      '</div>';
}
add_filter('img_caption_shortcode', 'add_attachment_data_in_caption', 10, 3);
</code></pre>
<h4>Generate thumbnails of all PDFs in the media library</h4>
<p>You can generate thumbnails of any already-uploaded PDFs.<br />
Activate the plugin and Click “Generate Thumbnails Now” link in “settings”. (v1.3.3 or later)</p>
<h4>Change attachment link attributes</h4>
<pre><code>function pigen_filter_attachment_link ( $html, $attach_id, $attach_url, $attach_output ){
  $attach_title = get_the_title( $attach_id );
  $html = '<a class="link-to-pdf" href="'.$attach_url.'" rel="attachment wp-att-' .esc_attr($attach_id). '" title="'.esc_attr( $attach_title ).'" target="_blank">' .$attach_output. '</a>';
  return $html;
};
add_filter( 'pigen_filter_attachment_link', 'pigen_filter_attachment_link', 10, 4 );
</code></pre>
<h4>Change thumbnail attributes</h4>
<pre><code>function pigen_filter_attachment_output ( $attach_output, $thumbnail_id, $thumbnail, $size, $align ){
  $attach_output =  '<img src="'. $thumbnail[0] .'" alt="'.get_post_meta( $thumbnail_id, '_wp_attachment_image_alt', true ).'" width="'. $thumbnail[1] .'" height="'. $thumbnail[2] .'" class="'.( $align ? 'align' .$align. ' ' : '' ). 'size-' .esc_attr( $size ). ' wp-image-'.$thumbnail_id.'" />';
  return $attach_output;
};
add_filter( 'pigen_filter_attachment_output', 'pigen_filter_attachment_output', 10, 5 );
</code></pre>
<h4>Modify imageMagick’s Settings</h4>
<p>Filters allow you to add your own modify imageMagick’s behaviour by hooking.</p>
<p>Sample usage for imageMagick user.</p>
<pre><code>function pigen_filter_convert_file_basename( $file_basename ){
  $file_basename = str_replace( '.jpg', '.png', $file_basename );
  return $file_basename;
};
add_filter( 'pigen_filter_convert_file_basename', 'pigen_filter_convert_file_basename' );

function pigen_filter_convert_imageMagick( $imageMagick, $before_name, $after_name, $max_width, $max_height ){
  $imageMagick = "convert -density 150 -quality 80 -background black -flatten {$max_width}x{$max_height} {$before_name} {$after_name}";
  return $imageMagick;
};
add_filter( 'pigen_filter_convert_imageMagick', 'pigen_filter_convert_imageMagick', 10, 5 );
</code></pre>
<p>Sample usage for imagick extension user.</p>
<pre><code>function pigen_filter_convert_file_basename( $file_basename ){
  $file_basename = str_replace( '.jpg', '.png', $file_basename );
  return $file_basename;
};
add_filter( 'pigen_filter_convert_file_basename', 'pigen_filter_convert_file_basename' );

function pigen_filter_convert_imagick( $imagick ){
  $imagick->setImageBackgroundColor( 'black' );
  $imagick->setCompressionQuality( 80 );
  $imagick->setImageFormat( 'png' );
return $imagick;
};
add_filter( 'pigen_filter_convert_imagick', 'pigen_filter_convert_imagick' );
</code></pre>
<h4>Automatically save image/PDF as featured image</h4>
<p>Automatically set PDF thumbnail as featured image.</p>
<pre><code>function save_pdf_thumb_as_featuredimage ( $post_id ) { 
    if ( wp_is_post_revision( $post_id ) ) return; 
    if ( get_post_type( $post_id ) !== 'post' ) return; // set your post type
    if ( get_post_meta( $post_id, '_thumbnail_id', true ) ) return; // post already has featured image
    $attaches = get_posts ( 'post_parent='.$post_id.'&numberposts=-1&post_type=attachment&post_mime_type=application/pdf&orderby=menu_order&order=ASC' );
    if ( $attaches ): foreach( $attaches as $attach ):
        if ( $thumb_id = get_post_meta( $attach->ID, '_thumbnail_id', true ) ){ // if pdf has thumbnail
            update_post_meta( $post_id, '_thumbnail_id', $thumb_id );
            break;
        }
    endforeach; endif;
}
add_action( 'save_post', 'save_pdf_thumb_as_featuredimage' );
</code></pre>
<p>Automatically set first image/PDF as featured image.</p>
<pre><code>function save_thumbnail_as_featuredimage ( $post_id ) { 
    if ( wp_is_post_revision( $post_id ) ) return;
    if ( get_post_type( $post_id ) !== 'post' ) return; // set your post type
    if ( get_post_meta( $post_id, '_thumbnail_id', true ) ) return; // post already has featured image
    $args = array(
        'post_parent' => $post_id,
        'post_type' => 'attachment',
        'numberposts' => -1,
        'post_status' => null,
        'orderby' => 'menu_order date',
        'order' => 'ASC ASC'
    );
    $attaches = get_posts($args);
    if ( $attaches ): foreach( $attaches as $attach ):
        if ( $attach->post_mime_type == 'application/pdf' ){
            if ( $thumb_id = get_post_meta( $attach->ID, '_thumbnail_id', true ) ){ // if pdf has thumbnail
                update_post_meta( $post_id, '_thumbnail_id', $thumb_id );
                break;
            }
        } elseif ( preg_match("/^image\//", $attach->post_mime_type ) ) {
            update_post_meta( $post_id, '_thumbnail_id', $attach->ID );
            break;
        }
    endforeach; endif;
}
add_action( 'save_post', 'save_thumbnail_as_featuredimage' );
</code></pre>


PDF Image Generator

Also ties in really nicely with the media uploader, the image is set as the 'icon' field of the attachment, as one would want. PS The feature for generating images for existing pdfs is at the bottom of the settings - scroll down to see (unlike me the first time)!

Super stuff. Works perfectly.

Very impressed with how quick and easy it was to get up and running with the generated pdf views.

Great Little Plugin

Generate automatically cover image of PDF by using ImageMagick. Allow user to insert PDF link with thumbnail into editor and set as Featured Image.

Automatic Thumbnail Generator vs PDF Image Generator