How I built a free browser-based watermark remover using Canvas API

I recently built CleanMark — a free, browser-based watermark removal tool that runs entirely in your browser with no uploads, no registration, and no cost. Try it here: https://cleanmark.org ## The core idea Most watermark removers send your image to a server. CleanMark does everything locally using the browser's Canvas API — your image never leaves your device. ## How Canvas inpainting works The technique is called inpainting — filling in a selected region based on surrounding pixels. Here's the basic flow: User selects the watermark area with a brush or rectangle tool The selection becomes a mask (white = remove, black = keep) For each masked pixel, sample neighboring non-masked pixels Fill the masked area using a weighted average of those neighbors The sampling strategy matters a lot. A naive approach just averages nearby pixels, which creates a blurry patch. A better approach uses patch-based matching — find a similar texture patch elsewhere in the image and copy it in. For CleanMa