The Mil installation should come with an examples folder.
There should be a link to this in the Mil Control Center app.
The MdigProcess.cpp is a good example.
A list of image buffers is setup to use in a ring or circular way by the capture callback function. Each time a new image is acquired, the callback is invoked and you can query which image in the ring buffer is the latest captured image.
Be aware that there are threading and timing issues here. The callback is in a separate thread and if your frame rate is high, then there is not much time to process between frames. At 50 fps, there is only 20 ms to process a frame.