IMG maps can be two things. Normally we talk about a Garmin map container file like "gmapsupp.img". It can also be a img file (like "0000004.img" for a single map tile in MapSource.
It's possible to build a IMG map container with MapSource and you can select which map segments/tiles that you want and even mix from different installed map products.
Try to view IMG files (booth types) with [Only registered and activated users can see links. ] to get a feel of whats inside.
If you have a map installed as a MapSource map and it shows up in BaseCamp, then you can use MapInstall or MapSource to transfer the map to your Oregon unit.
The IMG versions are ready to be copied directly to the GPS unit. If it's locked then it must be unlocked with a unlock key or some unlocker like the one in this thread.
New maps with MapID >= 2200 needs the GMA digital certificate for authentication in devices with newer firmware. In that case one needs to use an unlocker to remove the locking mechanism from the IMG file. The unlock code just unlocks but doesn't authenticate the map then the product is GMA aware.