I tried to get some magnets done for my recent FEs using my own image (photo) of the Disney Magic's bow which has an image of Mickey on it.
I went through the make a customised fridge magnet process, adding dates and titles, with Zazzle.com - however, after submitting my order for 10 magnets I got an email back a short while later saying they had cancelled my order as they considered there were copywriting issues witht the image I had supplied.
So yes, you could run into issues.