Mike Garrett

I just went through this recently. Check it out:

for file in /path/to/files/*/*.jpg; do sudo convert $file -resize '480000@>' -density 72 $file; done

480000 = 800*600 so all images will have the same image area without killing files that are 1200x200 or something ridiculous like that.

https://gist.github.com/MikeNGarrett/9774888