Which is best image optimization tool for Magento

For online, use this website
https://tinypng.com/

 

How does it work?

When you upload a PNG (Portable Network Graphics) file, similar colors in your image are combined. This technique is called “quantization”. By reducing the number of colors, 24-bit PNG files can be converted to much smaller 8-bit indexed color images. All unnecessary metadata is stripped too. The result: better PNG files with 100% support for transparency. Have your cake and eat it too!

In the above image the file size is reduced by more than 70%. I have excellent eyesight but can’t spot the difference either! Use the optimized image to save bandwidth and loading time and your website visitors will thank you.