In normal Photoshop, I would use the rectangular marquee tool, use control+a (is that option+a on a mac?) and then right click (control+click on a mac, for sure) and select stroke.
After that, you can choose a stroke setting. You'd want to use the 'inside' setting. You can also set size and color.
No way to mass produce them although I found a program for another member who wanted to do something similar. Lost track of the link (I don't use it), but here's another link that I found.
I'll post/edit if I find it.