Very recently facebook enabled the new facebook photo viewer, you can read more about this feature here. Yesterday we discovered another new feature rolled out with the new facebook viewer which allows you to make a profile picture for your facebook account. As shown in the snapshot below, you will see the option to make a profile picture mostly on the photos which contains people in it.
Following are the steps illustrated below to how to use this new feature and a make profile picture for your account.
Once you click the option on the new facebook photo viewer which will be shown on the bottom left corner, you will be redirected to another page where you will need to crop the portion of the image which contains you and then click done cropping as shown in the image below.
Once you are done with cropping, it will set the cropped section as your facebook profile picture for the account you logged in with.