You can do the following on C4D (prob in 3ds too)
Select a view and right click
Then U look around on the popup menu for a space to put a image as background
Put the corresponding view of a glock
e.g. Put right side of glock in right camera
Then point-to-point model until it looks more like a glock.
If im not mistaken the rear of the glock has 2 holes like this
u got the mesage