Gallery has the ability watermark images or entire albums of images. This is done by overlaying an image on top of another image.
Limitations:
NetPBM does not support steganography like ImageMagick. Therefore, only visible image watermarking is supported.
Gallery does not store the original image. When an image is watermarked, it is permanent, and can not be undone. It is assumed that the user will archive any images that they want without a watermark.
Only .gif, .tif, and .png are supported watermark file types. These formats support either a transparent color (gif) or an alpha channel (tif and png).
The size of the watermark, in pixels, is the same for the full size and resized images. In proportion to the entire image, the full size image's watermark is smaller. This could be a problem when printing the images.
To use watermarking...
Enable watermarking by entering a watermark directory in the Configuration Wizard under the "Locations and URLs" tab--fill out a directory containing the images you want to use as watermarks. Use the full system path. When logged in as admin, you will now see [watermark album] as an option in each album. If you that option, you will be presented with a page showing you the possible watermarking options.
Note that all files located in the watermark directory you defined earlier will now be available in the dropdown below the image. All you need to do to add a new watermark picture is to add it to the watermark directory, re-open the watermarking page and select it in the dropdown. The preview button enables you to preview the watermark before applying it, helping you visualize how it's going to look.