Samuel Wood (Otto)

Normally when you upload an image to a WordPress site, it creates several differently sized versions of the image automatically. Themes can define custom image sizes as well, increasing the amount of images generated on your server.
This plugin changes the way WordPress creates images to make it generate the images only when they are actually used somewhere, on the fly. Images created thusly will be saved in the normal upload directories, for later fast sending by the webserver. The result is that space is saved (since images are only created when needed), and uploading images is much faster (since it’s not generating the images on upload anymore).
“Pretty” permalinks must be enabled for this plugin to function.
Note: This plugin does not work on multisite setups, due to the way WordPress handles file serving in such situations (with ms-files.php).
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Dynamic Image Resizer

Make your images change sizes dynamically.

mhazami

With this plugin installed, you could resize images on the fly. just define the size and the way that you want to resize then it’s done. 
it is perfect for wallpaper and stock photography websites.
Features of plugin include:
<ul>
<li>support different images formats. (PNG, JPG, JPEG, GIF)</li>
<li>Intelligent sizing – No image distortion!</li>
<li>Resize by exact width/height. (exact)</li>
<li>Auto determine – let the script determine how to handle it. (auto)</li>
<li>Resize, then crop, with the exact size and no distortion. (crop)</li>
<li>Automatic download after resize.</li>
<li>Powerful shortcode.</li>
</ul>
<h4>Languages</h4>
<ol>
<li>English</li>
<li>Persian (Farsi) – <a href="https://github.com/iazami/picowall/wiki/Function-Reference" rel="nofollow ugc">(راهنمای فارسی)</a></li>
</ol>
<h4>Notes</h4>
Automatic download works with a wide range of devices and browsers.
You can expect it to work for the vast majority of your users, with some common-sense limits:
<ul>
<li>Devices without file systems like iPhone, iPad, Wii, et al. have nowhere to save the file to, sorry.</li>
<li>Android support starts at 4.2 for the built-in browser, though chrome 36+ and firefox 20+ on android 2.3+ work well. 
*Devices without Blob support won’t be able to download Blobs or TypedArrays</li>
<li>Legacy devices a[download] support can only download a few hundred kilobytes of data, and can’t give the file a custom name.</li>
<li>Devices without window.URL support can only download a couple megabytes of data</li>
<li>IE versions of 9 and before are NOT supported because the don’t support a[download] or dataURL frame locations.</li>
</ul>
<h3>Function Reference</h3>
there is two way to use this plugin, function, and shortcode.
<h4>shortcode</h4>
if you’re not familiar with programming. then use picowall shortcode to setup the script without programming knowledge.
shortcode attributes:
<ul>
<li>size (required) – you should at least define a width and height but also you can define multiple sizes (width,height,option|width,height,option|… width,height,option).</li>
<li>option (optional) (default:auto) – define the way that you want to resize (auto|exact|crop) if you don’t define this attribute then the script will automatically decide how to handle it. 
keep in mind that this attribute will make a global effect on each size block that you didn’t define an option for it.</li>
<li>sep (optional) (default: non-breaking space ” “) – with this attribute you can define a character to separate output links from each other.</li>
</ul>
examples
resize to exact width/height: [picowall size=”800,600″ option=”exact”]
resize to exact width/height (multiple size): [picowall size=”800,600|1920,1080″ option=”exact”]
resize then crop the first one and then for other ones just resize to exact width/height and then separate the results with a dash (pretty cool huh ?!)
picowall[size=”800,600,crop|1920,1080|150,150″ option=”exact” sep=”-“]
you can see that I use a different syntax in the last example. that is a “sizing block”. 
 it means that you can define multiple sizes with different ways to resize. simply just define it like this:
with,height,option|width,height,option| …. width(n),height(n),option(n).
note: use a vertical bar (|) to separate the size block.
keep in mind that if you don’t define the option for a sizing block then the value of “option” attribute will effect on that block. and also if you don’t define it there, then the script will automatically decide how to handle resizing.
<h4>functions</h4>
picowall($size,$option,$id)
this function will return an array of links to download resized images.
parameters
<ul>
<li>$size (required) – just like the shortcode you can define setting blocks too</li>
<li>$option (optional) (default: ‘auto’)- same as option attribute in shortcode.</li>
<li>$id (optional) (default: null) – if you use this function outside the loop then you have to define the id of post that you want to fetch photo from.</li>
</ul>
picowall_generate_links($size,$option,$sep,$id)
this function will print the result of above function in HTML.
parameters
<ul>
<li>$size (required) – just like the shortcode you can define setting blocks too</li>
<li>$option (optional) (default: ‘auto’)- same as option attribute in shortcode.</li>
<li>$sep (optional) (default: non breaking space ” “) – same as sep attribute in shortcode.</li>
<li>$id (optional) (default: null) – if you use this function outside post loop then you have to define the id of that post which you want to fetch photo. 
u want to fetch photo.</li>
</ul>

Dynamic Image Resizer vs picowall