Question: how to know if someone viewed your profile picture on whatsapp?
Answer: WhatsApp — Who Viewed Me works on Android 2.3 and above versions.
It has an easy to use interface.
Just download and install it, open the app and click on the “SCAN” button, let it run for a few seconds and it will shortly show the users who have checked your Whatsapp profile in the last 24 hours.