Hi there,
Assuming that each image's author, comment, etc, are generated by the person who uploaded it upon uploading, for something like that, you need to store the data either in file or database.
But if you are trying to do something more sophisticated than just to tile up the thumbnails, etc, I would recommend that you use database because it's more efficient that way.
Re MySQL installation, it really depends on what you mean by "my server package". If you have a shared server space, it's unlikely that you can install it, but you could ask whoever the provider of this server space is to install it. If you have a VPS or dedicated server (server of your own), then yes you can install it at your will (and risk). You can go to
http://www.mysql.com/ for more information about MySQL.