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.

Plagiarism may not affect you directly in this course but doing nothing increases the likelihood it will affect you in another course.

As a result of doing little or no work in one course, this student can possibly invest more time in another course in which you are also registered, thereby affecting your comparative level of performance.

Now... there is a caveat here: getting photos from someone is not plagiarism in itself. There is nothing to prevent students from looking at posts on SE for hints or indications on how to proceed with solving a problem.

The situation you describe becomes a plagiarism situation when the work submitted by a person is not his/hers, and when this person gets credit for this work without properly acknowledging the source of this work.

You should report what you saw through the appropriate channels, but stay away from accusations and keep in mind that the recipient may not have used the information.

The question of morality–is it right or wrong–that you pose is one that can only be determined by you. Some people might give you the opinion that it's never right to, for example, break the law; others are more lenient with exceptions. Ultimately, it is an exercise for you to discover your "moral compass."

In terms of the practicality of doing the report. No, it is not out of line for you to report. However, keep in mind that cheating is a very severe matter in most universities and your allegations will (or should) prompt the professor to conduct an investigation. It is likely that your professor will have to involve your friend (who took the pictures) both to uncover the student who took advantage of the answers, as well as her for facilitating them. The results of the investigation will depend on the approach your professor takes. If he/she is able to simply deduct that cheating occurred by looking at the two submissions, then perhaps you won't have to sit through a student conduct committee. However, if more evidence is required, be ready to testify against them in front of a committee (if your school utilizes one for such violations).

Finally, as mentioned in one of the comments, the impact of their academic integrity violation does affect you. In the long run, it can impact the quality of the course, the perception of your undergraduate program, etc.