bishopfox/unredacter

Unredacter is a tool by Bishop Fox, a security research firm, that demonstrates why pixelation is not a reliable way to hide text in images. The project exists to show that pixelated text can often be recovered if you know a few things about the original, such as the font and the size of the pixel blocks used. The core idea is that pixelation averages the colors of nearby pixels together. If you know the font the text was set in and can replicate the rendering conditions closely enough, you can run every possible character through that same averaging process and compare the results to the pixelated image. The character whose averaged output most closely matches the target pixel block is likely the original character. Doing this across an entire word or sentence lets you reconstruct the original text. Using the tool is a manual process. You crop the image down to just the pixelated region, measure the pixel block size, and then painstakingly adjust CSS in a test HTML file to replicate how the original text would have rendered. Getting the font, letter spacing, word spacing, and font weight right is the hardest and most critical step. Once those settings match closely enough, you select a character set to try and press a button to start the comparison. The tool is written in TypeScript and runs as a local web app. Setup requires Node.js: run npm install and then npm start. The project author notes the process is rough around the edges and not built for general-purpose use. The README is brief, but a full technical writeup explaining the method is available on the Bishop Fox blog. If you are a security professional reviewing whether pixelation adequately protects sensitive information in screenshots or documents, this project gives a concrete answer: it does not.