How to make a line pointer with text above the image using SVG?

Trying to find the plugin which helps me to create "stroke pointers", or "line tooltips", or "dimensions referencers" over images (tried to google all of this stuff with no luck), found only http://krispo.github.io/yarrow/ but i didn't realize that how to change apearance of markers on the end. Also, i'm not sure about scaling for mobile devices using Yarrow. And, maybe some more simplified alternative exists?

Sample image