Compress 90% of your photo size no quality lost

Compress and optimize your images

Up to 90% file size reduction

Compressor.io is a powerful online tool for reducing drastically the size of your images and photos whilst maintaining a high quality with almost no difference before and after compression.

http://compressor.io/compress

http://imageoptim.com/

can be achieved also with

optipng -o 3 foobar.png

   optipng in.png -o 5 -strip all -out temp.png
    pngout -f6 -kp -ks temp.png out.png

For jpegs, use jpegrescan.

    jpegrescan -s -t in.jpg out.jpg

see full reports on how to achieve this with:
https://news.ycombinator.com/item?id=7781956