On the back of the picture most people have one bit of wire/string, you can use two bits of wire/string the same lengh with lops on one end to go over hook/screw/nail If your house is not level then make one wire/string longer than the other
Random idea but - how about using a small piece of self adhesive E-profile draught excluder on each of the bottom two corners to provide a bit of frictional resistance
good god! for a moment there i completely misread the name of the thread! i cant tell u what i thought it said but im very relieved it wasn't what i thought it said! goodness gracious