What about the idea to integrate registering of graphic filetypes (bmp, jpg, png, etc.) to DO Viewer via setup or settings?
I think it's already on the to-do list. Something I'd like to see as well (also for Rar files etc.).
People can use the Open With menu to associate images with d8viewer.exe though so it's not essential, but it would be nicer to be able to associate them all at once, in one place, for sure.