How to open files one by one?

Question

Python

Good afternoon. Faced such a task, there are images, it needs to be compared with all the images in this folder until it finds a similar file. Under the conditions that the images in the folder change constantly. The difficulty for me is that I have no idea how to make this cycle so that it does all this one by one, that is, it compares, does not fit, the next picture, and so on, until it looks at all the pictures. Preferably a python example or a link to learn more about this cycle
Thanks in advance!