How can I meassure the length of a line in pixels?

Hello! I would like to meassure the length of a line in pixels from a specific image. Actually, I know that in "physical world" is 10mm. What I have done until now, was to convert the image into binary format and then try to detect the line by examine all of the bits and some of the neighbours. This way is extremely slow. Any suggestions?

PS. The line that am interested is the blue one on the piece of paper. Also, define a ROI by cropping a frame near the line is not an option because the location of the piece of paper is not fixed. Plus I m interested in an automatic method, not tools from apps such as rulers etc.

[Kevin Chng]

how about this way?

https://www.mathworks.com/help/images/measure-distance-between-pixels-in-image-viewer-app.html

[Dimitris Anastasiou]

Thanks for the quick response. The thing is that I am interested in an automatic way. I forgot to mention it in the description.

Answer 1

[Rahul punk]

https://www.mathworks.com/matlabcentral/fileexchange/70220-rahulpunk?s_tid=prof_contriblnk