This can certainly be done with a few lines of VBA code, but I'm not completely clear on how you want this to work.
1. Do you have 3 separate jpeg images, one for each color light?
2. Do you want them to appear inside the cell? If so will you size the cell (row and column) so that the cell is big enough to contain the image?
3. If you want them to appear outside (next to) the cell, then cell size is not an issue. But then will the user ever need to access the cell that is overlapped by the stoplight image?