Images in this category are images stored in Facebook album and imported into Phoca Gallery, see:
See documentation: Displaying Facebook Albums
If the size of thumbnail or image is different from Phoca Gallery settings, then Phoca Gallery will try to correct the size. If you will use Phoca Gallery for displaying Facebook images, it is recommended to use the same size of thumbnails for Phoca Gallery which is used in Facebook. You can set the background images to fit Facebook size. See Styling Background Images article.