Pixelation replaces local detail with blocks of averaged colour. It can create a mosaic style or make a background less detailed. Its privacy value depends on far more than the size entered into a form.
Image Pixelation lets you choose a block size. That setting is measured in source pixels and applies to the entire image.
Match the block scale to the source
A block size of 12 has a different visual impact on a 400 pixel wide image than on a 2000 pixel wide image. More blocks remain across the larger source, so it can retain more recognisable structure.
The output dimensions do not change. Pixelation changes the appearance inside the existing grid rather than generating a lower resolution file.
Average colours are drawn into the blocks. Large shapes and contrasts can still reveal what the original contained, even when the smaller texture is gone.
A mosaic can still expose information
A face may remain recognisable from its outline and surroundings. A short code may be guessed from context. This tool does not evaluate whether the result satisfies a privacy or legal requirement.
For material that must be removed, use a suitable redaction workflow that overwrites the relevant pixels and verify the final file. Do not rely on a decorative mosaic as proof of removal.
Keep the original separately when making a design effect. A later resize can change how the block pattern appears, so inspect the sequence of operations you intend to use.
For a batch, review each result rather than assuming one block size works equally well for every source. The correct visual choice depends on the image's dimensions, content and final display scale.