What happens with the photographs you are uploading to these sites? Do you still own the content? Are there any issues with copyright?
The answers to these questions are available in the terms of service (TOS). These aren't found in the apps themselves, but are easily found on their websites. They are rather long, complex documents although I think some effort (especially in the case of Historypin) has been made to avoid legalese and use common language.
|public domain image|
In regards to copyright, the most dangerous thing you can do is upload an image that you didn't take, and for which you don't hold copyright. By uploading it to the site, you are claiming it as your work, so you'd better make sure that's really what it is!
Also, better not modify an image in any way - don't use a photo editor to paint the town hall red and then post it to the site! Not having read the TOS is not a good defence if you've breached copyright...
One annoying thing they tend to say in the TOS is they can change it at anytime, so check back regularly. They really hold all the cards, don't they?