How to create IMAGE thumbnails

Howdy,

This ought to be a painfully simple problem and I'm sure there's a solution somewhere... if anyone has wisdom, please share! 

1 - I have lots of photos

2 - I'd like to generate a bunch of square thumbnails, one for each

Yeah.  That's it.  As usual, the Internet has proven useless.  No matter what I search for in terms of generating IMAGE thumbnails, all results (even if I add "-youtube" or "-video") are for video thumbnails.

Any tips - including unrelated freeware, etc., are much appreciated.  What I do *not* want to do and am already perfectly capable of is opening each image, one at a time, reducing its dimensions, and cropping a square out of it.  That seems needlessly burdensome in this day and age.  

Thanks in advance for any help!

Mark