Reposts are a moderator’s worst nightmare, and video reposts are especially hard to stop. Traditional bots only check a single thumbnail, so spammers easily bypass them by trimming a second, cropping the frame, or adding some frames to the beginning. Change the video thumbnail, and the bot is blind.

To solve this, I built DejaRepost: A Devvit app that actually watches the whole video to catch video reposts (even if the reposted clip has been trimmed, cropped or re-edited), while also stopping image and text reposts.

How DejaRepost catches video reposts:

• Instead of checking a single thumbnail, DejaRepost fingerprints one frame every second across the entire video.
• Sliding Window Matching: DejaRepost doesn’t just catch reposts through strict frame-by-frame alignment: each frame is compared against a local time window of surrounding frames, so that trimmed, cropped, or padded versions of the same clip are still caught.
• The fingerprinting is done using a perceptual hashing algorithm.

DejaRepost also catches image reposts (even if they’re cropped or altered!):

• Images are compared using visual similarity algorithms rather than exact file hashes.
• Crops, color shifts and other edits will not bypass detection unless the crop is severe.

Finally, DejaRepost catches text reposts by comparing their titles:

• It uses lightweight hashing to instantly check post titles and text against past submissions, catching exact copies and stolen titles.

What happens when DejaRepost detects a repost:

• It will report the post
• It will send you a modmail giving you: the link to the reported post, the link to the past post it matched it with (evidence), and a confidence score
• You can choose whether or not DejaRepost removes any reposts it detects (off by default, you can turn it on in the app settings)

DejaRepost requires almost no setup, no extra work from subreddit members, and all you have to do is watch the modmail as it detects reposts. It fits seamlessly into most subreddits, and it's perfect for video/image heavy subs.

Here’s the app link: https://developers.reddit.com/apps/dejarepost

Note: DejaRepost fingerprints your recent posts automatically in the background after install, so detection accuracy ramps up over the first little while.

If you have any questions or bug reports or feature requests, feel free to comment below or let us know through modmail. Alternatively, you are welcome to make a post in this subreddit.