After re-reading this, I think I misunderstood your question. Yes, you can take a folder that's on your computer (I have Windows, so that's all I know, BTW) and drag that folder into the Dropbox folder. Or, you can copy the folder and paste it into the Dropbox folder.
The beauty of the interface that Dropbox has with your computer is that it is as if you have the Dropbox folder right there on the computer, just like any other Windows Explorer folder. You can delete from it, copy, paste draws in, drag out, etc.
Two things about dragging a folder with your 80 pictures in it to the Dropbox folder on your computer: (1) It will take time for those 80 pictures to upload to Dropbox. No one can access them via Dropbox until that upload is done. That's why I usually do any big Dropbox moves at night, so it's done in the morning (cause it can take hours). And,
(2) If you drag a folder into the Dropbox folder, it will actually move that folder to Dropbox; those pictures will no longer be on your local computer's hard drive, they'll only be in Dropbox. So, if you want a local copy, may I suggest you do a copy and paste, instead.
I hope this clarifies it a bit more. And, I hope we've actually managed to answer your question!
Marilyn