Google+ Image Collection
Google+ unlimited uploads is great! The problem is that you may not know if the computer Auto Backup feature is working. One way to check this, if your not at the computer where Auto Backup is being run, is to check the Google+ image stats. You can find this information if you check out Google+ Account dashboard:
This page will display all sorts of stats about your Google account, including how many email messages you have in Gmail. Scroll down a bit to see the basic information on your Google+ Photos.
If you click on the word 'Google Photos' you'll see more details about your photo collection on Google+. This is a very useful page! For some odd reason, Google makes it hard to find. There's also good information on Gmail and other Google settings.