Is there a way for me to easily find and mark with a dot the center point of an image/photo?
I have no specific requirements for what software to do this (though I currently only have access to Gimp and Photoshop CS3, I am willing to install others).
I prefer solutions that allow the following (but they're not hard requirements):
(1) I prefer it to work on Windows, Macs, and Linux machines.
(2) I prefer to mark the center point "non-destructively", i.e. I still like to have the original image without any marks (maybe through layers?).