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.
I agree. If the image is without that label in a project, that is perfectly fine if that is explained in a "license.txt" file, and optionally in the metadata. But if that image is posted, for instance, in a forum, without a "license.txt" or metadata (or something similar) indicating the clearly the license and authors, that would be wrong. I may have done things in the wrong way in the past though, but we all have to try to do things in a good way.
Edit: @froggy77: by the way, i like so much your version of the spider that I think we should include it in CoS. Thanks for sharing your work!