I use the Flickr photo sharing service for several community web sites I manage where several members of the group may want to add photos to a common group photo pool.
Those photos are then available on Flickr but can also be mirrored on the web site.
For example, my son’s Pack 179 Cub Scouts have a Flickr page at http://www.flickr.com/groups/pack179/pool/ and the most recent photos from the pool are also published to http://www.pack179.com/?page=Photos
If I send you an invitation to one of these groups, just follow the instructions to create a Flickr account. If you already have an account with Yahoo, you can use that (Yahoo owns Flickr).
You then follow the instructions to upload photos through the browser-based user interface, which should be fairly self-explanatory. You don’t have to worry about resizing photos because Flickr does that automatically. There is also a desktop software program called the “Flickr Uploadr,” which I will describe later.
Once you have uploaded your photos, you will be prompted to add captions and tags. Tags are just labels make it easier to search and find photos later. So you might add “PinewoodDerby2010″ as a tag on all the photos from that event.
Uploading photos makes them available in your “photostream,” which you can view on your Flickr home page. The next step is to add them to the group pool (in this example, the one for Pack 179). That part is not documented as well, which is why I’m writing this.
There are actually two ways. First you can click open up the page for viewing an individual picture, and then click the the “Send to Group” button. It looks like this:

Using the "Send to Group" button
Alternatively, you can select “Organize” off the menu and send a whole batch of photos to the Group. The Organizr utility shows all the available photos on a ribbon at the bottom of the screen and allows you to drag and drop selected images into the work area at the center of the page. This is what I’m talking about:

Using the Organizer to Select Photos ...
Again, you choose the “Send to Group” option at the top of the page and pick the group you are targeting.

... and send them to a group photo pool
As I mentioned, there is also a desktop software upload tool for Flickr, which you might want to take advantage of if you use the service frequently. Here’s the download page, and here’s what it looks like:

The Flickr Uploadr lets you drag-and-drop photos from your computer, add captions and tags, and upload them as a batch