Kay Joe

Important Aspects
<ul>
<li>The default featured image will show exactly how your theme shows it. That is if it appears besides the excerpt it will show there. It will not show on top of the excerpt or misaligned, as this plugin only changes the image and does not add any html attributes.</li>
<li>This simple plugin sets an image that has been already uploaded in the WordPress Media Library as the default Featured Image for all posts that do not have a featured image already set.</li>
<li>This plugin can also remove or unset an image that exists in media library and is set as featured image for one or more posts. This is the remove default featured image feature.</li>
<li>Your theme must already support post thumbnails for this plugin to work. This plugin will show the default featured image you set in same style and position as shown by your active theme. Only the image will be changed</li>
<li>If you are using a cache plugin, try disabling it and clear browser cache to see results. You can always go to a post and see whether the featured image has been set or unset.</li>
<li>Please deactivate any other featured image plugin before using this plugin. Also, if you have modified the code in your theme files to show a default featured image then please delete that code, else plugin will have problems</li>
<li>The following steps are recommended but not necessary.These may be required to set the size for the default featured image.
<ul>
<li>To Set a default featured image for a post, check the size of the featured image that your theme is showing. This can be dome by right click on the image->Choose view Image OR copy its link or address and open in new browser. Right click on the image and see its dimensions in image information.</li>
<li>If your theme’s functions.php file uses the add_image_size function and the size of the image uploaded to media library to be used as default featured image, is higher than the max size set for thumbnail by any of the _add_image_size_then the selected image to be set as default image will be resized and saved as a new image with size as the maximum size set to be used as thumbnail (not single post) by those functions.</li>
<li>It is recommended that the Settings of the small thumbnail in the Settings-Media and the size set by add_image size be kept same
<ul>
<li>After that please resize the image to be set as default featured to the smaller size (to optimize page load time) or resized exactly as the dimensions of smallest size in Settings->Media as set by the add_image_size function</li>
<li>Then uploaded the image to the media library and set it as default featured image using this plugin</li>
</ul>
</li>
</ul>
</li>
</ul>
<h4>Suggestions are welcome</h4>
<ul>
<li>Found a bug?</li>
<li>Something to be improved?</li>
</ul>
Contact me @kayjoe on WordPress.org or ano[dot]shani[at]gmail[dot]com

Default Featured Image Themed

Set an uploaded image as a default featured image for all posts without a featured image. Remove an image set as featured image for one or more posts.

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Scott Bressler

Feel free to get in touch with us about anything you’d like me to add to this plugin or any feedback. We love hearing from our users! <a href="https://wordpress.org/support/plugin/media-credit/#postform" rel="ugc">Start a thread on the plugin forum</a> and we’ll get back to you shortly!
This plugin adds a “Credit” field when uploading media to posts and displays it under the images on your blog to properly credit the artist.
When adding media through the Media Uploader tool or editing media already in the Media Library, this plugin adds a new field to the media form that allows users to assign credit for given media to a user of your blog (assisted with autocomplete) or to any freeform text (e.g. courtesy photos, etc.).
When this media is then inserted into a post, a new shortcode, <code>[media-credit]</code>, surrounds the media, inside of any caption, with the provided media credit information. Media credit inside this shortcode is then displayed on your blog under your media with the class <code>.media-credit</code>, which has some default styling but which you can customize to your heart’s content.
You can also display all the media by an author on the author’s page. See more in the <a href="https://wordpress.org/plugins/media-credit/faq/" rel="ugc">FAQ</a>. 
Options
This plugin provides a few options which appear on the Media page under Settings. These options are:
<ul>
<li>Separator</li>
<li>Organization</li>
<li>Display credits after post</li>
</ul>
Example
This is best explained with an example. With a separator of ” | ” and an organization of The Daily Times, media inserted will be followed with a credit line appearing as follows, with the username linking to the author page for that user:
<a href="" rel="nofollow ugc">John Smith</a> | The Daily Times
Further explanation
Separator: These are the characters that separate the display name for a user on your blog from the name of the organization, as described below. The default separator is ” | ” but feel free to change this to suit your needs.
Organization: This is what appears after the separator as listed above. The default organization is the name of your blog.
Display credits after post: With this option enabled, media credit shortcodes will not appear by default when inserting media into your posts. Instead, the plugin will look through the content of your posts for any media attachments and display something like the following at the end of each post with the CSS class .media-credit-end:
Images courtesy of <a href="" rel="nofollow ugc">John Smith</a> | The Daily Times, Michael Scott and Jane Doe.
In this example, John Smith is a user of your blog, while the latter two credits are not.

Media Credit

Does exactly what is asked of it, resources for developers, what more could you ask for?

Thanks to this plugin

Adds a "Credit" field when uploading media to posts and displays it under the images on your blog to properly credit the artist.

Default Featured Image Themed vs Media Credit