Import multiple photos from Dropbox to iMovie?
If you have a PC/Mac and use iTunes, it would be a lot quicker to do this using the File Sharing feature for apps.

Here are the steps to do this, taken from the Apple iMovie help documentation at "iMovie Help for iPad: Import from iTunes":


  
  Connect your device to your computer, then open iTunes on your computer.  
  In your iTunes library, select the device near the top of the iTunes window.
  Click the Apps button.
  Select iMovie in the Apps list below File Sharing (you may need to scroll to see it).
  Do one of the following:
  
  Drag the file you want to add to the iMovie Documents pane.
  Click Add below the iMovie Documents pane, and in the window that appears, navigate to the file you want to add.
  
  To copy the file to your device, select the file, then click Open.
  The file appears in the iMovie Documents pane when copying is complete.