Magic Lantern is a 3rd party firmware that can enable many features on your Canon DSLR that are not natively available out of the box. Everything from focus peaking, to zebras and even HDR video can be achieved with the use of this firmware.
Another handy feature is the firmware's ability to instantly tell you you camera's shutter count!
In order to do this, follow these easy steps...
1. Make sure you have the latest and greatest Magic Lantern installed.
2. Turn on your camera, and access the Magic Lantern menu.
3. Scroll to the "Debug" tab and you will see your "Shutter Count".
Your shutter count will be the total number of pictures taken + number of LiveView actuations.
The camera I'm using as a test for this has about 5,000 actuations. Pretty fresh!