You are using the version that integrates with 15 different forums it is called Photopost Pro.
PhotoPost PHP Photo Sharing Gallery - Product Details
Our details page lays out the differences and the other downloads clearly state
vb only which is vbGallery not Photopost Pro.
I can not tell you whether you will lose data or not. Your photo ownership will be messed up since users will not have the same userid in the forum if they even exist at all.
You need to install Photopost into the same database and table prefix as it currently resides. You can try running this script to realign userid's once your done but this expects those users with those usernames to exist in phpbb3. Obviously that would depend on your site whether or not you lose anything
Reassign userid's when switching integrations to VBulletin