Is it reasonable to report another student for cheating when it has no impact on me?
As others have already mentioned, cheating is wrong and it's the right thing to speak up when someone commits a wrong. It may also indirectly affect you when someone cheats (eg. through grade inflation).

However, by reporting the cheater you are also implicating your friend who passed on the photos and facilitated the cheating. Your friend might feel upset (and perhaps rightly so) that you didn't put your friendship above some general (and perhaps minor) moral obligation. I caution that your obligation to report is not unconditional in the sense that you have to accept a disadvantage for yourself, such as a spoiled friendship. Moreover, I would argue that you also have an obligation of loyalty towards your friend; whether or not that 'trumps' your obligation to report depends on how close your relationship is.