When you select "Choose Folder or Disk...", the choose dialog that appears will not allow you to select your iPhoto Library, which is located in your ~/Pictures folder by default.
You need to select a folder or disk, and iPhoto Library is neither. It's a file package.
Here are two ways of handling this:
1. Select the parent folder of iPhoto Library, which is your Pictures folder by default. If you do not want to backup everything in your Pictures folder and you are using Deja Vu on Mountain Lion (10.8) or higher, you can add exclusions in the Options > Exclusions tab. See the following knowledge base article if you are using Deja Vu on an older version of OS X:
Excluding certain items from a backup
2. Create a new folder and move iPhoto Library inside of it. Then select that folder in the 'Where' column of Deja Vu. See this Apple support article for more information:
iPhoto: How to move the Library folder to a new location