It has a clever plugin system that allows users to extend it with new functionalities. Fiji (Fiji is Just ImageJ, http://fiji.sc/) is a distribution of ImageJ, that includes (amongst other things) a lot of plugins, some useful libraries and an updater to keep...
You could try the free Comic Kit plugin on Adobe Exchange (https://exchange.adobe.com/apps/cc/13159). After you install it, do the following 1. Choose Edit > Fill2. Choose Content: Pattern3. Check the check box next to Script: under Options4...