1. Add a Photo to LinkedIn

5. LinkedIn's Photo tool wants a square image!
Their square template is sized to the smallest dimension of your original photo image.

8. A simple method to modify your original image with Paint Image Editor (Part of Windows) This works with either Wide or Narrow Images

12. Another Method This also works with either Wide or Narrow Images

18. Comments Posting a photo is a very personal decision.
It can certainly help jog the memory of an acquaintance. I admit that I remember faces better than names.
It might help you market toward your job-search goals.
In the past a photo has been key to a profile's strength rating. I, however, see that my profile is rated 'All-Star' and I have never posted a photo.
(Oh by the way) – How about a relaxed SMILE!