Hosting company

[Useless]

Depends how they define hits. Some people [wrongly] refer to a single page load as a hit, but really, that's a visit. Some people refer to every element of your page as a hit, as in each thumb, banner, etc would be considered a separate hit. That's correct.

A "hit" is actually a "successful request to your web server from a visitor's browser for any type of file, whether an image, HTML page, an MP3 file, or any other type. A single web page can cause many Hits -- one for each image included on the page, etc." ²

Therefore, if a single web page contains 20 images, that's 21 hits - 20 images plus 1 for the page itself. If one single person looks at 10 web pages which contains 20 images on each page, that single individual is responsible for 210 hits.

from http://www.kylake.us/www101/what_are_hits.htm

Hits
Any request made to the server which is logged, is considered a 'hit'. The requests can be for anything... html pages, graphic images, audio files, CGI scripts, etc... Each valid line in the server log is counted as a hit. This number represents the total number of requests that were made to the server during the specified report period.

from http://www.lamphost.net/node/716


Consider that bolded portion when forecasting the amount of hits your gallery would expect per day. Also, I agree that you don't want a host that would shut you down when you are seeing heavy traffic, since that's the time when you want your site to be running its best. If it was a DDOS attack, that would be another issue.