Uploading a picture to Foodspotting, Google Local and Yelp at the same time

Storing this in cookies/session is the way to go. In PHP you can just use the $_SESSION functionality to do this. More info on that here.

This will not work if the user opens a private browsing session, though. IP tracking would work, but IP addresses change due to ISP assignments and may represent different users (for example, two users in one home sharing the same DSL connection). For these reasons this is not recommended.

From Google's help page

1. Make sure you've claimed one of the listings in Google Places. Verify that there’s only one active listing in your account by logging in to your Google Places account.
   1. If there's more than one listing in your account for the same business, you’ll first need to fix that problem by following the steps in the section below.
   2. If you don't have a listing for it at all, you should claim your business.
2. For every extra result for your business, go to its Place Page, click the Report A Problem link, and select "Place has another listing". If you can, include a link to your claimed Place Page in the comments section.
3. Google will review these reports and fix duplicate business listings.