Most games can’t be played from images. It’s called copy protection and it’s to prevent you from playing the game if you don’t have the original discs.
Also, from my experience, you can install from one drive letter and play from another. For instance, if you installed disc 1 from drive E, then when the game runs it will check drive E for the disc. So having disc 1 in drive E and disc 2 in drive F may not work anyway. And you don’t need both discs mounted at the same time.