Image, fonts and portfolio rights

Hi there, I’m currently working on a portfolio to showcase my graphic design work. many designers just starting out, I’m creating quite a few mock projects; this allows me to demonstrate the breadth of my skills across a variety of assignments. Since I’m using mock projects and the portfolio isn't for commercial sale, am I free to use any images or typefaces I like? I ask because I see a lot of mock posters on Pinterest where designers have fun creating their own posters for movies, concerts (Charli XCX, Daft Punk, etc.), and so on. I’d love to hear about your experiences! :) (I publish here because not allowed in the graphic design thread)