OK thank you, glad that it please
No, it isn't worth it. The nickname can be put in the interface Solarus since it is easy now to add the author(s) and the license in the projects. In the end, in my opinion, it is necessary to cut the images without the licenses and the authors in order to avoid having too big files in the final project.
If I add my nickname and the CC-BY-NC-SA license (or another license that I don't understand) for the 100% homemade stuff, it's just to avoid a bit of seeing my work on old-school games for which some makers are trying to grapple 1€. A small "thank you" in the credits is enough and fun, otherwise I don't care about the nickname in the image.
When I edit an image, it means that I liked it a lot and I just add "edited by" to respect the original author: if my result is ugly and I leave only the name of the author without the "edited by", I think she or he will not be happy.