program to calculate measure in a image

[endarion88]

the title may be confusing so i will explain better.

i'm looking for a program that help me figure real misure (centimeter/meter) from a image for exmple: i load a image and trace line and i specify said line is = 40cm after that if i trace other segments the program will calculate the proportinal lengt of said segments or something similiar

for more info and use of what i need: i'm a sword freak and i want something that help me figure a sword proportions from a picture with no reference