Imagemagick recursively reduce files to < 800x600 and 72ppi

bulk-resize-script

# This is a bash script meant to be run on the command line. Requires imagemagick (apt-get install imagemagick)
## THIS WILL OVERWRITE YOUR FILES, uses sudo and may not require it.
for file in /path/to/files/*/*.jpg; do sudo convert $file -resize '800x600>' -density 72 $file; done

### another method using resolution (800*600)
for file in /path/to/files/*/*.jpg; do sudo convert $file -resize '480000@>' -density 72 $file; done

### example of *not* overwriting files
for file in /path/to/files/*/*.jpg; do sudo convert $file -resize '800x600>' -density 72 converted-$file; done