ETC and using any JPG's in the 'grabs' folder

New here and interested in the ETC.
After reading the manual, it looks like there is a folder called ‘grabs’ that stores screenshots. These files are standard jpgs and I was wondering if you could load any jpg in the folder and use it with the ETC?


Please forgive this question. I should’ve looked further at the forum comments to find info about using still images.