I have specified in wpForo to "Insert Forum Attachments to Media Library" and indeed I do see my images there. However, the orignal images are also saved in wp-content/uploads/wpforo/default_attachments/. In order to save on storage space, how do I get wpForo to only store images in the Media Gallery? Thanks!
The images that you have uploads with wpForo are stored only at wp-content/uploads/wpforo/default_attachments, wpForo also allows managing those images from Media Library, but they are not stored at the Media Library only shown there for managing.
If you check the file URL from media library, you will see that the image's physical storage is ...default_attachments.