Seednin

It's a sneaky one. I tried to catch it in the ActivityMonitor process list -- but it pops into existence for only a second or two when an image is first mounted. Too quick to inspect. But unix always provides a solution (or three). Try this in Terminal.app:
sudo find / -name ' DiskImageMounter'
/System/Library/CoreServices/DiskImageMounter.app
/System/Library/CoreServices/DiskImageMounter.app/Contents/MacOS/DiskImageMounte r
/System/Library/CoreServices/DiskImageMounter.app/Contents/Resources/DiskImageMo unter.scriptSuite
/System/Library/CoreServices/DiskImageMounter.app/Contents/Resources/DiskImageMo unter.scriptTerminology
BTW, the 'sudo' prefix is optional -- it just avoids cluttering-up the output with a gaggle of 'permission denied' error messages. If you don't have admin privileges, redirecting stderr to the bit bucket will do the same:
find / -name ' DiskImageMounter' 2> /dev/null
...in the beginning was the command line,
Looby