Gallery has the ability watermark images or entire albums of images. This
is done by overlaying an image on top of another image.
NetPBM does not support steganography like ImageMagick. Therefore,
only visible image watermarking is supported.
- Warning: Gallery does not store the original image.
When an image is watermarked, it is permanent, and can not be un-done.
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.