Since nobody seems to have even touched on this detail but this is popping up in search results...
I'm not a lawyer, but my understanding, based on what I've read in free game development resource communities, is that, as long as you don't combine the image and non-GPLed stuff in the same file, it counts as aggregating the image and code, not making one a derivative work of the other.
(The most common context I've seen this in was people wondering whether it was legal to use GPLed code and CC-BY-SA art assets in the same project.)
In other words, as long as your GPLed image is a separate file from your non-GPLed stuff, it's legal for the same reason that it's legal to distribute a magazine CD or DVD containing both GPLed programs and programs under GPL-incompatible EULAs, even if you have a pretty Autorun launcher menu that can start either one.
Aside from that, you'll want to include proper attribution in your About dialog, manual, or wherever your standard place for that is.
(A good rule of thumb is to include the work's name, creator's name, a link to wherever the version you are using was originally posted, and a mention of the license under which you're using it. (ie. "GNU GPL 2.0-only", "GNU GPL 2.0-or-later", "GNU GPL 3.0-only", "GNU GPL 3.0-or-later", etc.))