Concretely, the mark is composited with proper alpha blending and written back losslessly, which is why a lossless format is the right place to keep a watermarked master you will export from repeatedly. 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. BMP is essentially raw uncompressed RGB rows with a small header, so it is perfectly lossless and enormous — often 10-20x the size of the same image as PNG. That governs how cleanly a semi-transparent mark can be blended into the underlying content.
Anything specific to BMP worth knowing?
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Yes — because nothing is compressed, a BMP is fast to read and edit but punishing to upload, and it carries no metadata to preserve. 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.
