If your Reddit posts are getting silently removed, duplicate detection is almost certainly the reason. Here is exactly how it works and what you can do about it.
Reddit computes three types of perceptual hash for every image uploaded. pHash uses a mathematical transformation called DCT (Discrete Cosine Transform) to create a 64-bit fingerprint of what the image looks like. aHash scales the image to 8x8 pixels, converts to grayscale, and compares each pixel to the average brightness. dHash compares brightness between adjacent pixels to detect gradients.
When you upload an image, Reddit computes all three hashes and compares them to previously uploaded images using Hamming distance — the number of bits that differ between two hashes. A Hamming distance below the threshold (typically 5-12 out of 64 bits) means the images are considered duplicates.
Renaming the file does nothing. Changing format (JPG to PNG) does nothing. Adjusting quality or compression does nothing. Adding metadata does nothing. All of these change the file but not the visual content, and perceptual hashes are based on visual content.
Pixel-level modifications: random noise injection, DCT coefficient modification, color channel shifting, micro-cropping, and invisible watermark patterns. These changes must push the Hamming distance above the detection threshold while remaining invisible to the human eye.
This is what spoofing tools automate — generating a version with a completely different hash in under one second.