The quickest way to delete all the photos from an iPad running ios 7 is to use the Image Capture program.

  1. Open Image Capture
  2. Connect you iPad to your Mac with USB cable
  3. Click on the iPad icon top left
  4. Select all by using ⌘A (or select manually if you want to selectively delete)
  5. Click the red circle symbol on the bottom and confirm you want to delete.

After a few seconds or minutes depending on the size they will be deleted from the iPad.