You should normally contact the respective blog admin as the rules change from blog to blog.

That aside, you can always create a free flickr account and upload your photos there

and then link the flickr page. This way you instantly get a URL :)

As soon as you have the flickr account setup and your photo uploaded, you can check this out to see how to link your entry:

http://blog.inlinkz.com/2014/02/how-to-add-images-from-flickr/