Date: 28 February, 2017
Your profile picture has to reflect your chosen niche, if you are a brand make your profile picture your logo.
If you are an individual it is preferable that you use a selfie but if your account doesn't feature selfies then whatever image that is most related to your niche is the appropriate one to use. You want the image to be exciting and interesting enough for people to want to click into your feed and follow you.
Test out a number of profile pictures to see which one has the highest like and follow rate. This will give you an idea of what your audience really wants to see. The target audience should be interested enough to investigate your account further and follow you permanently.
TIP: Apply this same exercise to the images on your feed. Which images are getting the most likes? Stick with similar images for your feed.