As the above link is no longer active, here's the text from WATCHOUT v5.5 release notes:
In addition to loading images from a file on disk, or from the Dynamic Image Server added in WATCHOUT version 5,
you may now also load an image from a URL. This is similar to loading images through the Dynamic Image Server in
that the image will be loaded afresh each time it's displayed, allowing images to be easily updated.
The URL you specify may refer to an actual website on the Internet (e.g., a weather map), or may point to an in-house
web server used only for serving images to WATCHOUT.
To use this feature, first determine the URL of the image to be used.
This can be done using a web browser by right-clicking the image and choosing "Copy Image Location", or similar command.
This gives you the image URL.
Open a new browser window and paste in the URL (which typically ends in .jpg or .png) to make sure you get just the image.
Determine the dimensions of the image, in pixels, by dragging the image onto your hard drive and opening it using an image editor.
In WATCHOUT, choose "Add Image Proxy" on the Media menu, paste in the URL of the image, and enter its dimensions.
If the image contains transparency, select the type under "Transparency". Click OK, then use the image as usual in WATCHOUT.
Each display computer will load the image from the URL every time it's displayed.