Hi. I have a flickr account with some images on it. Would adding a link to my site in the image descriptions be helpful? Or are they completely nofollow just like a link in the comments section would be?
It would definitely help your website. Even if the backlinks were nofollow, it's always good to have a mix of dofollow and nofollow backlinks. I would say 80/20 in terms of dofollow and nofollow backlinks. Having backlink diversity is important due to the new Google algorithms so try having a mix of different backlinks.
Agreed, the users above me put it nicely. All backlinks will have a bearing on your rankings to some degree, and diversification of these backlinks is something Google wants to see. I've heard that linking to and from social networking sites this way, alone, can greatly influence your rankings, so try this with other networks, too.
I do have a flickr account which I usually post images on it. I think it won't be useful in SEO terms but I'm sure its helpful to get traffic from people visiting the image. Some people are interested to see more of the images so they'll click the link below it.
I am not an expert as far as Flickr is concerned but if the link is an actual hyperlink and is visible without logging into the site then it should count as a backlink. unbel has given excellent advice here; try to get links from as many types of sites as possible without worrying about Do-Follow and No-Follow links and you can expect good SEO juice flowing towards your site. Link diversity is now more important than ever so it makes sense to get links even from unusual sources (like image sites).