Watermark a photo without uploading the original

Watermarking is the last thing you do before a photograph becomes public, which makes it the last moment to think about what the file carries. Two separate jobs meet here: marking the picture so uncredited reuse is obvious, and clearing the record of where and when it was taken. A watermark does the first and nothing at all about the second.

Be realistic about what marking achieves. A discreet mark in a corner is easy to crop away; a large one across the middle survives cropping and damages the photograph. Photographers generally accept that a watermark deters casual reuse and stops nobody determined, which is a reasonable trade if you choose the strength consciously rather than by default.

Placement is the practical decision. Put the mark where removing it costs the person removing it something, usually across a part of the image that matters, rather than in a corner that a crop discards. Size it to the image rather than to the preview, because a mark that reads clearly on a large photograph becomes an illegible smudge once the same file is shown as a thumbnail. Keep the unmarked master, because a watermarked file is a distribution copy and you will want to make another one.

The check is worth doing in this order: watermark the photo, then open the result in the EXIF viewer. You will see the marking ran locally, with no network traffic, and you will see the coordinates still sitting there, which is the point the page is making.