A watermark is a deterrent, not a lock. Anyone determined enough can remove one, and the tools for doing it have got considerably better. What a watermark reliably does is make casual reuse awkward and make the source of an image obvious wherever it travels — and for proofs, drafts, and work sent to a client before payment, that is usually the entire job.
Understanding which of those two things you want changes where you put the mark.
Placement decides whether it works
A small mark in a corner is the most common choice and the weakest one. It is trivially cropped out, and cropping a corner rarely damages the picture. If your concern is someone lifting the image and using it as their own, a corner mark barely slows them down.
A diagonal mark across the middle is much harder to remove because it sits on the subject — you cannot crop it away without cropping the thing that made the image worth taking. A tiled mark, repeated across the whole frame, is harder still: there is no rectangle of the image that does not contain part of it.
The trade is legibility. The stronger the protection, the more the mark interferes with viewing the picture, which is exactly what you want on a proof and exactly what you do not want on a portfolio piece. Filum offers diagonal, horizontal, and tiled layouts, each in light, medium, or strong strength, and in a neutral gray or a warning red — so you can choose deliberately rather than accepting one default.
What stamping costs your file
Drawing text onto an image changes pixels, and for JPG, WebP, and AVIF that means the file has to be re-encoded. There is no lossless way around it — those formats cannot have new content drawn into them without being rebuilt. What a tool can do is re-encode at high quality and tell you the measured quality of what it delivered, rather than leaving you to guess whether your watermarked proof is now visibly worse than the original.
PNG behaves differently: every pixel the mark does not cover stays exactly as it was, and transparency is preserved.
A watermarking tool should also not change your format. A JPG should come back a JPG. Turning a photograph into a large PNG because it was easier to write is a common shortcut, and it triples the file size for no benefit. Filum keeps the format you gave it, and preserves transparency in PNG, WebP, and AVIF.
Why the upload matters more here than almost anywhere
Think about which images actually get watermarked. Photographs sent to a client before invoicing. Design drafts under NDA. Product shots ahead of a launch. Documents marked CONFIDENTIAL or DRAFT. Images being shared precisely because their distribution needs controlling.
Every one of those is an image where the un-watermarked original is the sensitive artefact — and an upload-based watermarking service receives exactly that, before it does anything else. You hand over the unprotected file in order to be given the protected one.
Filum draws the mark inside your browser on your own device. The image never leaves your computer and never reaches a server, so the unprotected original is never anywhere but where it started.