Both used in and used for are correct in this context. Used in is correct here because in is used to describe something that is enclosed by or inside of something else. Print media refers to printed publications such as newspapers, magazines and books. Since print media are enclosed objects (because print media has pages), a photo can be in or inside of print media. Used for is correct here because for implies the purpose of something, and here the purpose of the photo is for it to be in print media.