I had a debate with my friend about this topic because he had a photo captioned:
Seth and I playing lion king
and I said it should be
Seth and me playing lion king
Which is correct?
You can't really insist on one or the other being correct, because you are not working with a complete sentence. I think the best you can do is to recognize that the majority of English speakers would use "Seth and me."
Even if you add the implied initial phrase that would make it an entire sentence ("This is"), you still wind up with some debate. "This is I" is formally correct (i.e "This is Seth and I playing lion king"), but the vast majority of English speakers consider it pompous and awkward, and still would use "me."
It has to be “Seth and me playing lion king” as the title of a photo. Imagine it without Seth there at all: you would always, only, and ever label that photo “Me”, never “I”. Since the case of a pronoun never changes when you add in somebody else with an and, we arrive at “Seth and me playing lion king” as the only right answer.