I use this software to do the simple stuff like cropping and resizing:
XnView
Plus it has really cool batch processing options.
So to crop the images to a 4:3 ratio, go to Edit -> Set Selection Ratio -> 4x3
and then the selection will be 4x3 and voila
Later on when you're ready to publish you can re-size them all to a consistent size.
I notice there that you have some frames that are pretty narrow compared to the others so you'll probably have to sacrifice some of what you intended the reader to see there when you crop, that sucks. For that pyramid, I would cheat by just resizing and ignoring the "maintain aspect ratio" thing, just stretch that sucker out and see if it still looks good
It's good software, and it's free
Oh and btw, 4x3 is just one option, you can do whatever you want of course!!

5x3, etc you can even make the frames square if you want, or if you just can't sacrifice anything on those narrow ones you can just pad the canvas (resize canvas), just as long as all the frames are the same size
