software recommendation - Mac app to compare processed image before/after?

I often use ImageOptim and ImageAlpha to optimize images. ImageAlpha has a really nice feature because it lets you compare optimized image to the original one before saving it. Is there a software that does exclusively this (comparing two images) in a convenient way?

Answer

Not in any specific order.

1. Kaleidoscope - $70 ( Mac )


2. PixCompare - $4 ( Mac )


3. Pixel Diff - $2 ( Mac )


4. ImageDiff - $2 ( Mac )


5. Araxis Merge - $150 _{^{give or take}} ( Mac and Windows )



6. Image Comparer - $35 ( Windows )


7. Image Diff Tool - Free ( Mac, Windows, Linux )


8. Beyond Compare - $30 (Mac, Windows, Linux)


9. Resemble.js Free ( Web application )
   
   
   
   • I was thinking that if you wanted to, you could pretty easily extend the functionality of this with a comparison jquery plugin or something, to extend what it can do, like this for instance.