If you include a photo of a football player or a club crest, the person reviewing the portfolio will know that you didn't create them. That's fine.
When looking at applicant portfolios, i see a lot of (usually lads) creating the kind of graphics that clubs put on their social feeds. Often they demonstrate good technical skills, which is important, but attempting to replicate/copy existing work isn't really what Universities are looking for. We want to see original ideas, not pastiches of what's already done. So as a general piece of advice - when creating this kind of work for your portfolio - make it look radically different to anything you've seen before online. Challenge the conventions.