There are two differences I can think of. One is that “portray” can have a meaning that “depict” doesn’t have and that is “to play the role of”: “Laurence Olivier portrayed Hamlet beautifully.” source https://www.merriam-webster.com/dictionary/portray The other is that portray seems to have more to do with an artistic representation. So if we are talking about a photographic representation I think the normal choice would be “depict” and not “portray”, as in “The cover of the magazine depicted Senator Kerry and Bin Laden shaking hands”. or "The photograph depicts the two brothers standing in front of a store."

Portray is a synonym of depict. The difference is that portray is to paint or draw but depict is to render a representation of something, by words, sounds ,images and so forth. Depict means describe but portray means paint draw.