I love Google. Google enables people from all over the world to find my site. Sometimes however, my site promises more than it delivers. Take my Boston Photos category for example. Visitors come I here, I think, expecting to find a vast photo archive with access to photos from all neighborhoods and streets and various buildings etc. (An aside to the person searching for "photos of the Boston Massacre": you must be the student I had about ten years ago who believed people in the 19th century had stereos). Needless to say, I don't have a vast archive of photos. I occasionally pull something out of my personal collection that I feel might make an interesting subject, like the Louisburg Square doorway photo, but visitor requests far outweigh my capacity to provide.
That being said, today I'm going to direct people to four resources (which I've talked about before, I know) that have excellent collections of Boston images, and one Dorchester specific resource.
The Bostonian Society has many of their images viewable online, all of these institutions have excellent reference staff with whom I've worked in the past.
For Dorchester images, I recommend the Dorchester Atheneum.