Say you had a number of niche specific emails...
 

I have about 100 emails (I know, not many at all). They weren't opt in. The emails were collected from a guestbook on one of my sites...

Is there anything wrong (legally) with emailing them, thanking them for posting(2months later) and putting a link to a FPA or gallery in the email?

Wouldn't that depend on what kind of site Your guestbook is at..?

The more adult You're guessing those emailers are, the less wrong :2 cents:

Also, You could throw in something in Your mails telling them why they're receiving
Your mails and some way to opt out of them.

Hopefully You've found an additional source of the dollars :Graucho

you guys taught me that it depends on the country your sending from. :thumbsup