Creating own aerial images from an air balloon

there is a mapper in the wiki (he's in central europe if I remember correctly,but the post was in english) that I've read about that's been using kites or model planes to hoist his camera.he will have some experience, if I can find it again I'll post a link, found it http://wiki.openstreetmap.org/wiki/Vertical_Aerial_Photographs

We did a similar project in Stratford-upon-Avon in 2009, using a light aircraft. From that project my tips would be:

1. Don't worry about getting precise vertical photos, but anything less than 70° to the horizontal isn't useful enough
2. The longer the focal length of the lens the better (i.e. use telephotos). From the height you are flying you won't get much ground cover on each photo though.
3. You need a few ground control points on each photo, so you'll probably need some physical feature with corresponding GPX tracks (e.g. a road with a few corners) in each photo.

When you have the photos, you can use the processes described in the link above to warp them and get them geo-referenced, and then import them into JOSM for tracing.