Version 2.6 is a legacy release, and these documents are no longer being maintained.


A digital watermark is generally understood as a kind of marker embedded in a digital object (such as an image, text, video, or audio file), typically used to indicate ownership and/or to prevent unauthorized use. For images, the watermark is often a text layer or image identifying the owner of the digital object.

AtoM supports basic digital watermarking functionality for images and text files such as PDFs, since the preview image (aka the reference display copy) for a text file is a JPG image. The watermark does not alter or affect the master digital object. Similarly, thumbnail images, used in search and browse results, are also unaffected. Only the reference display copy, used on the view page of an archival description, will show the watermark.

AtoM’s default behavior is to composite (a.k.a. “tile”) new reference images with the watermark file. For best results, we recommend using a format for your watermark that supports alpha compositing, such as a PNG image file. The watermark will work best if the background is transparent or white - AtoM will render images used as a watermark transparent, so they need not be transparent to begin with.


You must have Imagemagick properly installed and configured for digital watermarking to work in AtoM. For more information, see:

Applying a watermark in AtoM

  1. First you will need to choose your watermark. You can use an institution logo, or create a simple text-based image. There are also many tutorials available online on how to create watermark images using open source tools such as GIMP. Choose something that won’t be too visually busy, so the underlying photo can still be seen clearly. Try to ensure the image background is white or transparent for best results. You also need to use an image format that supports alpha compositing - we recommend using images in a PNG format for best results.

    Additionally, because AtoM will tile the watermark until the entire reference image is covered, we recommend choosing an image no larger than 250 x 250px.

  2. Save your chosen watermark file as watermark.png and place it in your root AtoM directory.

  3. That’s it! Now any images uploaded in the future will have the watermark applied. If you wish to stop having watermarks applied, remove the watermark.png from AtoM’s root directory.

For more information on uploading and managing digital objects in AtoM, see:

Example output

For the following example watermarked image, the watermark used was a 250 x 250 pixel PNG image of the AtoM logo on a white background. The reference image to which it was applied (available in the AtoM demo site, here) was approximately 480 x 317px:

An exmaple reference image with a watermark applied

Applying a watermark to existing images

If you have followed the steps above, you can use the digital object derivative regeneration command-line task to regenerate your existing derivatives. As they are regenerated, AtoM will apply the watermark to any images generated for use as the reference display copy.

php symfony digitalobject:regen-derivatives

For more information on using this task, see:


When running the regen-derivatives task, all of your current derivatives for the targeted digital objects will be deleted - meaning ALL of them if you provide no further criteria. They will be replaced with new derivatives after the task has finished running. If you have manually changed the thumbnail or reference display copy of a digital object via the user interface (see: Edit digital objects), these two will be replaced with digital object derivatives created from the master digital object.

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