What is JHEAD and what does it do? (Why would I need it?)
JHEAD can extract information out of a jpeg picture that was taken from a digital camera. A date stamp would be an example of this. If your digital camera dates your pictures, then this function can allow those dates to be seen in PhotoPost. You do not have to use this if you don't care to see those types of things.
What is JPEGTRAN and what does it do? (Why would I need it?)
jpegtran performs various useful transformations of JPEG files. It can translate the coded representation from one variant of JPEG to another, for example from baseline JPEG to progressive JPEG or vice versa. It can also perform some rearrangements of the image data, for example turning an image from landscape to portrait format by rotation.
What is ZLIB compression and what does it do? (Why would I need it?)
You do not need this with PP 4 and later.
Your Commission Junction click-through URL
This is a way for your website to earn a little extra cash. If you sign up for this, when users click the link it is tracked back to your site and gives you credit for "advertising" PP on your site.
Forum database table prefix
If you have an external forum in use like phpbb, it might be configured so it's tables have a prefix in front of them. For example, the users table might look like phpbb_users. The prefix would be phpbb_. You would have to login to phpMyAdmin to see if yours are set up with prefixes and what they are, or check your admin panel of your forum software to see if you can find the setting there. If you are using PP internal registration, you do not need this setting.
Optional Photo Field #1-6 (blank for none)
You can add up to 6 custom fields for extra data on your photos.
In the admin Config page there are these fields I was hoping to have explained:
Path for MYSQLDUMP
MYSQLDUMP performs a backup of your databases. You will need to check with your host to find the path, or log into telnet or ssh and do a "locate mysqldump" if you have telnet or ssh access.
MySQL database backup directory
The location you which to have the data dumped to.
This is almost always set to "/" unless your forum system is set differently or you have problems with cookies. Leave it set to this unless you have problems.
IP Caching Timeout
This is used to "track" your users. If you don't want a user to come in and vote 1000 times a day you can set this to help limit that. It is also useful if you have a very limited amount of throughput and don't want one user to use that all up. You can change this as well as all the other settings at a later date.
Sorry, I can't remember what this is used for.
This page might help you as well: