I'm more concerned about text since images and video are easily detectable. The only way I know of that I can cheaply but frustratingly do is: Take the latest and last backed-up text, open them both in notepads, keep making one pop up to see "change" visually, erase any new lines from the latest text until there is no change, repeat as you scroll down, then check the text count in a online letter counter. This definitely 100% works, the correct letters and count are checked, but is time consuming and painful. What about saving any edits as two copies and then have a program check if they are exact? That should not be hard to make/get/run.
(I'm a linux person, so my answer is untested Google-Fu)
FC file1 file2
will provide you with the differences between 2 text files. (/B switch does binary)
More Googling found a freeware GUI to do something similar - http://windiff.en.lo4d.com/