Concretely, watermarking an icon is rarely useful — there are too few pixels for a mark to be legible without destroying the icon, so treat this as a stamp on the largest entry rather than protection. You control the position, the size and the opacity, and the same settings are applied consistently across everything you upload.
Can I use my own logo, or only text?
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Either. Upload a transparent PNG logo, or type text and choose the font, colour and opacity. A tiled repeat is available when one corner mark is too easy to crop away.
Does the file format affect how the watermark comes out?
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It does. ICO is a container that holds several square bitmaps at once (16, 32, 48, 64, 128 and 256 px) so Windows and browsers can pick the size they need. That governs how cleanly a semi-transparent mark can be blended into the underlying content.
Anything specific to ICO worth knowing?
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Yes — an ICO is a stack of square bitmaps, not one image, so operations apply to the stack and Windows still picks whichever size it wants. It affects when in your workflow the mark should be applied.
Does a watermark actually protect my work?
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It deters casual reuse and it credits you; it is not security. A corner mark can be cropped and a faint one can be painted out. If protection matters, a large semi-transparent mark across the subject is far harder to remove than a discreet one in a corner.
Should I watermark before or after resizing?
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After. Watermark the final deliverable at its final size, so the mark stays legible and proportionate. Watermarking a master you will process again means the mark gets resampled and compressed along with everything else.
