When I was doing research, I used photoshop a lot, mostly to annotate pictures and clean up the clarity on some. When I was first learning photo editing, there was a parody website that had people enter in mashed-up movie names: 2 or more movies having a common word (or part of a word) that then get blended together: "Night of the Living, Evil Dead" is mashed of "Night of the Living Dead" and "Evil Dead". And people could also create various things about the movie (tag-line, plot summary, memorable quote, etc.) including movie posters. So I had made a movie poster for "Remember the Titanic" (mashup of "Remember the Titans" and "Titanic"). It used a "Titanic" poster / cover which featured Leonardo DeCaprio in the sky (
http://img.movie2k.to/thumbs/cover-375928-Titanic-movie2k-film.jpg) and the poster from "Remember the Titans" that showed Denzel Washington. Then I used photoshop to cut out Denzel's face, changed the color of that picture to the sky-blue / gray colors from the Titanic poster, and replaced Kate Winslet's picture with this photoshopped Denzel, making it look like Leonardo was attempting to kiss Denzel. Everyone on the site like the picture, and thought it looked very realistic (I wish I still had that creation; I probably do somewhere in my computer
store hoard).
I really like the web-site PhotoshopContest.com. Each week they have a picture that others use to "chop" into their own creations, and then site members get to vote for their favorite picture. Some have been so good that I use the picture as a desktop background. It may be a good site to get ideas as to what is possible in Photoshop.