I know it's normal in a lot of European countries, but I don't know which way the Swedes roll.
Swedish Wikipedia does not mention a photo: https://sv.wikipedia.org/wiki/Curriculum_vitae
This website mentions that a picture is not required in the cover letter and does not mention the issue at all in CV: http://www.yourlivingcity.com/stockholm/work-money/living-sweden-swedish-cv/
From nearby countries, photos are not be assumed in academic settings in Denmark, Finland, or Norway (based on personal experience). They do seem to be more prevalent in German-speaking countries, which do have close cultural ties to the Nordic countries.
Overall, it seems that a picture is not required, but, according to a comment from xLeitix, it would not be unusual to have one.
No, it is not common in Sweden to add a photo on your CV. I have even heard that it is not advised. The reasoning I have heard was to keep the CV barebones and down to the facts. They should evaluate you based on whats on paper, rather than how you look. It goes a bit hand in hand with general Swedish approach of neutrality/objectivity.
In Denmark, on the other hand, it is almost expected to have a photo on your CV. The reasoning there, albeit anecdotal, is that when a hiring manager or a recruiter has your CV they know who to look for in a room/career fair etc. You sort of establish a first contact, of sorts.
That being said, in academic context, it does not really matter much. Most academic labs recruit internationally (at least on paper) and would not expect you to follow the local traditions in job applications.