A person has custody if he has actual physical control of the property but the person who has constructive possession has substantially restricted the custodian's right to use the property.
From the en.wikipedia.org
For instance, the bank must take constructive or actual possession of the good before selling it to the customer.
From the en.wikipedia.org
Note that this is different from larceny which simply requires that property be taken from the victim's possession, actual or constructive.
From the en.wikipedia.org
If the bribe is treated as held on a constructive trust then it will remain in the possession of the fiduciary, despite bankruptcy, until such time as the principal recovers it.
From the en.wikipedia.org
Chose in possession is opposed to chose in action, and denotes not only the right to enjoy or possess a thing, but also the actual or constructive enjoyment of it.