Now that you have Dropbox setup and working, you might want to upload some of your photos to your Dropbox account so you can access them from your PC or your other devices. To do this, you'll need to go into the Dropbox applications. Unfortunately, there is no way to upload to Dropbox from the Photos app.
First, tap the Uploads tab at the bottom of the screen. It is located between Favorites and Settings.
Next, touch the button with the plus sign (+) at the top left corner of the screen. Touching this button will drop down a menu letting you choose which photos to upload. If you have multiple albums, you will first need to choose which album and then you will be presented with a list of the photos.
Touch all of the photos you want to upload. You don't need to upload them one at a time.
Choose a folder at the bottom of the screen. By default, they will go into your Dropbox folder, but you may want to store your photos in a specific folder. You can even create a new folder from the menu presented after tapping the destination folder button.
Upload the photos. Don't forget to tap the blue Upload button at the top right corner of the upload menu. Tapping this button begins the upload process, and once done, the photos will be saved on the web and ready to be access by your PC or any other device with Dropbox loaded on it.