Flickr is a photo sharing site that allows people to organise and share photos. In 2008, 5% of British people with access to the internet used Flickr, making it the most popular photo-sharing site.
Upload any good photos you have on your charity and the projects it runs to Flickr. Don't worry if your photos aren't perfectly composed - I'm not a professional photographer either, but post a selection of the photos I take while doing PR work for charities to Flickr to publicise my services and the work of my charity sector clients.
For every photo you upload, include a title, description (including a link to your website) and tags describing the content. To give you an idea of the information you can include, check out the Acorn PR photo channel on Flickr.
Create a group for your charity or social enterprise on Flickr and invite your supporters to join the group. In addition, ask supporters to use a particular tag (eg. organisation-name) when uploading photos related to your charity. It's also worth joining relevant groups on Flickr, such as UK Flickr Users and Flickr's Charity group.
Other photosharing sites that you may want to look at include Photobucket and Webshots.