I didn't have a Google+ account so I quickly created one. I logged in and within a minute, I had my own account.
So how do you access Picnik via Google+?
Here's a step by step tutorial for you:
1. Create or Log In to your Google+ account.
2. At the top right of your screen is your profile picture. Click it, then click "View Profile."
3. Click Photos.
4. Upload New Photo.
5. Once your photo is uploaded, roll your curser over it and then click the pencil icon. This will launch Picnik! Use as you usually do!