The Filter Gallery uses Concrete5's built in file management system.  

After you upload your images in the file manager, you should add them to file sets.  Be sure to name your file sets something that's descriptive since the name will be used by the filter form.  You should also be sure to give each image a title and, if you'd like, a description. 

When you're ready to add the filter form to a page, just add it like any other block.  You'll be asked to check a box beside each file set that you'd like to include.  Each instance of the block can use different file sets.

If you have any questions or issues, please feel free to contact us and we'll help you out!