How to Crop and Convert all images in the directory and sub directories on Linux (command line)?

I have a main directory Pictures. Inside that directory there are hundreds of other directories. Inside those directories I have images. One main image and thumbnails generated from that image.

• I need to crop and optimize all these images.
• All images that have a width higher than 600px should be cropped down to max 600px. Other images should stay as it is.
• All images should be optimized

How can I do this? Im in a Ubuntu server. (Need to use commands)

I don't know the exact answer to your solution, but for batch command line image editing, I would look into imagemagick. http://www.imagemagick.org/script/index.php