image segmentation to calculate real length

Hi

I have an cylinderical object that enters in camera frame from one side and leaves on the other side. I am trying to measure the real length of the object but after binarizing the image the bottom part of the cylinder become part of the actual length which gives a wrong result(see the attached images). my question is how to exclude this bottom part to extract the real length? i have tried playing with different threshold levels but couldn't suceed. There are three images attached one the real object the other with fixed threshold level of 0.20 and the third one with threshold calculated with Otsu.

thanks!

Regards

Malik

[darova]

Can't you mesure top part?

[Malik Malik]

Thanks! I am trying to calculate the corners co-cordinates but the function "corner" is of no use as it produces corners in different places. any alternate?