From the site FAQ:

First you need to browse to the Gallery. Click on the "Gallery Links" on the menu and scroll down to "Upload Photos".

Uploading a Photo is accomplished thru the use of this form. By filling in the variables, you are telling PhotoPost which photo you wish to upload and information about the photo.

Choose a cateogry - select the most appropriate place for your photo using the drop down list of available categories.

Photo to upload - using the Browser button, select the file on your system you wish to upload (be sure that the file does not exceed size limitations)

You can also upload a ".zip" file containing multiple photos. You can do this by browsing to the .zip file rather than the actual photo as stated above.

Disk space remaining for your account - This tells you how much disk space you have left for uploads

On the next page you will be prompted to enter the following information for each image you uploaded:

Enter a title for the photo - This is a short description of the photo

Keywords - enter up to 10 descriptive terms people can use to search for your image

Photo Description - This area provides for a more detailed description of the photo

Do you want to be notified by email when users post replies? Check this box if you would like an email whenever someone posts a comment to your photo.

Supported image types include: JPG, GIF and PNG.
Support multimedia type (if enabled): MPG, AVI, ASF, WMF, MOV