For more irregular objects... (Score 1)

...there's a program called Snake Measurer which works pretty well. You just take an overhead photo (say of - oh, I don't know - a snake) and include something of a known size, like a ruler. Then you load it into the program, draw a line on your known object, enter the size of it and start placing dots on the subject you are wanting to measure. You end up with a length in the unit that you used for the known object. It's not 100% but it works pretty well. Best of all, it's free. As in beer. [Note: I have no attachment to the programmer(s) - I just have a snake to measure.]