This feature is available in FooGallery PRO Expert and PRO Commerce.
You can load galleries from other sources, including Media Categories. This means that you can select one, or multiple, Media Categories and all images attributed with these categories will appear in your gallery.
With FooGallery PRO Expert and PRO Commerce, you are able to assign categories to images when you upload them to the Media Library. Alternatively, you can access images already in your library and add categories. Here are some more details on this.
Once you have assigned Media Categories, you can use these to create galleries. This process is the same as for loading galleries from Media Tags. You can see a more detailed explanation of how to do this, in our article on Loading Galleries from Media Tags.