Here's a freeware I use all the time.... it's for creating thumbnails of pics. If you have PhotoShop or similar program this does it automatically when you open the pic with the program, but this freeware does all the thumbnails you want all at the same time. This is the easiest way, Just drop a pic or ton of pics in the window of this freeware program, and it does all the thumbnails for you... as simple as that.
(for Macs)
http://www.stalkingwolf.net/software/cocothumbx/