Blur / Pixelate Image

You set the region to hide as a box in pixels, measured from the top-left corner of the picture, and only that region is processed; the rest of the image is copied through untouched. Blur averages each pixel with its neighbours across a radius you set, so detail dissolves into its surroundings. Pixelation instead replaces blocks with their average colour, which is the more visually obvious of the two: it reads as deliberately hidden rather than as an accident of focus. The before and after preview shows whether the box landed where you meant, and to hide more than one thing you run the result through again.

Where it stops: Read this before relying on it for anything sensitive. A weak blur or a coarse pixelation can sometimes be partly undone, especially over text, because the original is still statistically present in the averaged pixels. The stronger the setting, the less there is to recover, but the safest option for something that genuinely must not be read is not to obscure it at all: crop it out, or cover it with a solid block. For documents, Redact PDF removes the content rather than hiding it.