Animal Control agencies and appointed shelters generally are the only legal way to establish abandonment and assign new ownership. Private citizens have no right to confiscate private property. The process may be simplified to facilitate rescue but private rescue organizations that deal in stray dogs and do not go through Animal Control are liable. Animal Control are usually required to keep records indicating a wait period, in Tennessee I believe state code is 3 days, and they must show that all means of contacting the owner have been exhausted. Where I live the animal must be held by Animal Control for 14 days.

I've seen owners have their pets "rescued" and then take the rescue organization to court in order to recover their pets. No one wins in that situation. It's even worse when the pet is euthanized minutes before the owner comes by to take their pet home.