No problem. If you go to your Dropbox folder, then "public", you'll be able to right click on a picture and get the public link. Once you have that link/address you can post the picture online. I copied and pasted the beginning part in my contacts, all the way up to the file name, for use whenever I need it (I just add whatever file/image name).
I don't have a computer with me so I transfer the images I want to post to my iPhone or ipad via an eye-fi card, then I edit the images and post using photogene2 for iPhone. It lets me upload multiple images to Dropbox. Works great.