I have been reading on other forums of new regulations on National Forest and BLM land consering trail cameras and leaving them unattended. One of them in Utah is that you can not place a camera on National Forest land before 2 weeks of a hunting season. This law has been on the books for a couple of years now but they are starting to enforce it. Also as I have said the BLM is picking up trail cameras when they are found and they consider them abandoned property after 72 hours.
So unless you are using them on private property you need to check with the local Forestry or BLM office before you place them if you expect them to be there when you go to get the pictures.