If you are using windows, you can use a tool named "astrogrep" (freeware) and by using the find function -inside files- you could, then, look for all the str files and find the "super1-5.bmp" inside of them.
Actually I did it by myself and I couldn't find any str file using that bmp file. So perhaps my data.grf is not updated, or maybe, the bmp file you are refering is hardcoded inside the str file.
