waugh

When you reblog a post, you'll put a static copy of it onto your blog, as I've done with my initial reblog of the gougar post. The original uploaded file (the doge picture) is thereby preserved in that copy of the post and in all reblogs of that copy.

Replacing the original uploaded image (the doge) with another file (the gougar) does not affect the copies shared already!

Now, while this can be used for jokes like this little prank, you might find it more useful for another purpose: tricking Tumblr's automated crawler that checks posts for NSFW content.

Using the same process, one can first upload the actual file (say, a picture of boobs), reblog it to get a static copy of it, then immediately edit the original post to change the picture to something SFW (say, a balloon animal). The crawler will only check the original instance of the post, and even if flagged, will unflag it if you repeal after changing the file.