What kind of blog? I mean here or is it blogger or something?
Generally you need to have a site to store your photos like Flickr. Flickr is free until you reach a certain number of photos or you buy more storage. I've never had to add any.
http://www.flickr.com/
If you use it you can click on the link in my sig about posting photos and it'll give you info about how to work it which may also work for other sites.