Format plugins will add support for image formats that are not included in the main release. About 35 image format plugins can be downloaded from that page. Most of them are exotic formats like jng, wic or bmf which most users probably never heard before.

The plugins can be downloaded separately or as a plugin pack and have to be unpacked into the XnView plugin directory where they will be automatically recognized by the image viewer.

Add-ons on the other hand add support for external services like Imageshack, Nero, archive or ftp support. It usually means sending pictures to another application or adding new functions in XnView like viewing images in archives or adding basic image editing support.

The add-ons and format plugins add new features and functions to XnView which could be interesting for some users.