When you add a picture to a contact, the picture will appear on the screen when calling or when getting a text message. To assign a picture to a contact on Galaxy S7 (Edge), do as follows:
1. Open the Contacts app on your S7
2. Find the contact you want to add a photo to, and tap to open it
3. Hit the Edit button on the top side of the screen to enable contact's editing mode
4. Touch the Camera button, next to the contact's name
5. There you have the option to take a picture using your camera (both front and rear cameras), or select a picture from Gallery.
6. Once you take/select a picture from camera/gallery, you need to crop the picture and fit it in to the Circle frame.
7. Tap the Done button and the new picture will be added to that contact