eaxjp

Image will be shrink in the case of automatic JPEG and PNG format to upload the image. 
There are the following features in isShrinker WordPress Plugin.
Can specify the maximum file size. 
Keep aspect ratio. 
Convert image inclination from inclination information of image
If you upload, such as iPhone app slope of image because reduced after correction 
it appears in the blog exactly as it appears in the iPhone.
The maximum file size of the image is 50KB by default 
Length of the long side of the image is 640px by default 
And it is with, but you can change from the management screen of WordPress.
Upload png image ‘watermark.png’ to plugin directory and then watermark will be enable. 
Watermark add on right bottom of image. 
If watermark enabled water mark transparency setting is enable.
<h3>Arbitrary section 1</h3>

isShrinker

When uploading, it will shrink the image automatically. The feature is  keeping the aspect ratio and  maximum file size can be specified.

Rickard Westerlind

Orangelab

Dramatically improve the quality of re-sized images by making WordPress use ImageMagick instead of standard GD image library.
Features
<ul>
<li>Preserve embedded color profile in re-sized image</li>
<li>Automatically recognize custom image sizes</li>
<li>Allow regeneration of existing images (optionally for selected image sizes only)</li>
<li>Configure image quality or use dynamically computed default value</li>
<li>Optimize different image sizes for either quality or size</li>
</ul>
Lnguages: English, French, German, Swedish, Turkish
Requires either ImageMagick binary or Imagick PHP module.
<h3>Contribute</h3>
Code repo available on https://github.com/orangelabweb/imagemagick-engine/

ImageMagick Engine

Maybe even better.  It uses ImageMagick Engine that is installed and allows me to easily regenerate all my images.

Works as advertised

The thumbnail regeneration could be a bit faster though. I have used it for longer than I can remember, at least 5 years.

Simple, functional

Improve the quality of re-sized images by replacing standard GD library with ImageMagick.

isShrinker vs ImageMagick Engine