Does anyone know of a group to whom I can post the following situation?

When do you legally, absolutely, need to have a subject's permission to run his or her photo on your website or brochure? Do I correctly recall that if the eyes of the person are obscured, I can use the photo even if I didn't get permission? If I didn't request permission, can I use the photo of someone whose eyes are closed? Whose eyes are obstructed a little by glasses?

Here's the situation: I am redoing a website and brochures for a client (myself) who, when not writing, editing, and consulting, runs a travelling farm of educational workshops. It is difficult to describe the bonding between visitors and animals, or between visitors and animal-based crafts, without using photos.

Having taken a year's hiatus, I haven't got any animals at the moment and so can't stage photos. I can't just go to the zoo and get some generic shots, either, as the workshops only work with animals raised with children.  Also, subjects need to work with the animals (or crafts) for a time and require a lot of introduction before they can "get into" the animal or craft; this can require extensive and expensive set-up, and you really can't predict the quality of the "chemistry" beforehand.  Any good photos of this work is therefore the result of much effort and caring and I would really like to use some lovely photos people have given me over the years, if possible. Note: all the faces will be close-ups because the photos' aim is to capture the expressions on the faces.

Case #1: My young son, a few years ago, captured some warm and special moments hard to duplicate at a workshop I taught at a Sunday school for Grandparents Day. Many relatives/friends attended. The teacher says she has no idea who the people in my photos are or how to contact them.

Case #2: Summer camp directors, etc., sometimes sent me photos of campers and animals or hands-on exhibits weeks after their visit; at the time, I neglected to request signed use forms (guess I was busy trimming hooves or slinging 50-pound bags of feed).

Case #3: One day a high school took photos of its students during my workshop, posted the photos to the school website, and gave me permission to link to their website.

Case #4: A local newspaper took photos of me, my sheep, and clearly recognizable high school girls for a front-page story, which I wish to show on my website.

Case #5: A girl whose face is somewhat turned away from the camera is hold a gosling, whose beak is peeking through her cascade of curly blonde hair.

Can I legally use these photos without tracking down the subjects and getting their permission?

The parents of three children whom I was able to track down all gave me enthusiastic permission to use the photos. I'm also using photographs of my own children, from when they were small. Murphy's Law would state that the best way to locate the remaining parents (and in one case, a grandmother cuddling my gosling) would be to publish the remaining photos on the web and in brochures and watch the irate parents pour out of the woodwork to sue me.  However, my website is intended to promote good feelings and not land me in jail. Can I legally publish the photos, wait for the subjects' parents to come forward, and then ask for their permission? Anyone ever face a similar problem? What can I do at this point?

Thanks for your help,