Reducing image size

[techlists at phpcoderusa.com]

Hi,

I have about 9GB of photos.  These images are 2560 X 1920 and are 
roughly 2mb each.  I assume I could get away with a much smaller image.

What size should I reduce these to?

During my research most suggest using ImageMagick from the command line. 
  Is this the best practice?

I'm sure I will want to use some type of script since I do not want to 
do this one by one.

Thanks in advance for your help!!

Keith