I don't think the OP is talking about image processing - they don't want to actually crop and save as a completely new image, I think they want to be able to choose which portion of the photo to display as a thumbnail/profile pic. So in the profile view, it only shows that one individual but when you click to view the full photo, it shows everyone. Likewise, you could then tag everyone else in the photo and for each person, it would only display their individual face but upon clicking to enlarge, they would ALL open the same full photo of everyone.
This is not image processing so much as it is an image display feature.
This is not image processing so much as it is an image display feature.