The export frame feature save the bitmap as 32-bit (so it's kinda inconvenient). The edited image must be saved as 24-bit BMP. Then you can mux with MuxMan and import into
DvdReMake.
There's a script that does the muxing for you. It's called
AutoMux that makes use of MuxMan. Follow the direction for installation and usage. Very handy for muxing multiple images.