Is there any way to allow someone to download the whole shared Photos folder on Dropbox and not only individual files? Preferable a solution that doesn't require the receiver to register on Dropbox? 
Download complete folder shared under Photos on Dropbox
dropbox
You could try this method posted on Mac OS X Hints:Just stick the folder of files into your public folder, and head to  the Dropbox webapp. Click on the folder you want to share, then click  the Get Link button at the top of the page. Add ?dl=1 to the end of  it, and send that link to your friends. Itll zip the file up for them  and download it to their computer. (Lifehacker synopsis)