You can do it with quickmemo, but it also works (even though it can be a little tricky) by pushing the power button and volume down simultaneously. I have an f7 and I've done it both ways.
at the top of your screen swipe down. You'll see sound, airplane mode, etc. With that you'll see quick memo click on it and it will show you what the pic looks like. Then you save it and will find it under your gallery app, there will be a quick memo that all the save photos go to