>>48895944Just do what I do.
Whenever I get a new image of /a/, I create 7 duplicates of that image. Then I open each up with an image editor, such as MS Paint or GIMP, and add a small black dot randomly on each one. This is invisible to the human eye unless you know where to the look. This way, if I ever want to post a file, I never get the duplicate image. Even if I want to post the same image more than once, I can do this, as I have seven unique versions. I don't create more than seven because it is unlikely I will need more than seven in the time it takes for a thread I have posted it in to 404 and because it'd be too time consuming as I do this with all images I get from 4chan.