One of your pictures shows a 50 mV reading. With a 10 Mohm input impedance, it takes about 5 nA to induce this voltage. This can easily be picked up by the leads. This problem is worse on some meters with an even higher input impedance. Even some cheap DMMs have a FET-input (Gohm impedance or so) mode on the lowest mV ranges.
This can actually be a real issue, and is the reason why some of the products aimed at electricians have a lower input impedance, or the ability to switch from 10 Mohm to a few kohm or so. If you're measuring the voltage between two wires, you may not have any way to check if they're connected. Capacitive coupling with other wires can easily give high (eg. 80V) voltage readings with 10 Mohm DMMs.