At Admin Panel -> Settings -> Switches in WSN Gallery you have an option to switch on Image Embed URLs. When enabled, this adds a spot on the listing details page below the image which will say "Embed/hotlink URL (600px):" and then show an input box with a URL filled in it. Your website visitors can copy and paste this URL in order to embed a 600 pixel wide version the image in forum posts, blogs, or wherever else they like. Essentially, it encourages hotlinking of your images -- this can be beneficial advertising if you've applied a watermark to thumbnail images at Admin Panel -> Settings -> Files.

If you wish to change the size of the embed urls, just go into the details template and replace 600 with the desired maximum width and 800 with the desired maximum height.

Note that it will always generate a cached .jpg style url instead of a .php url, even on the first view when a thumbnail cache normally wouldn't have been generated. This ensures that it can be hotlinked on forums that forbid dynamic URLs for security reasons (such as WSN Forum).