Image Analysis using manual or interactive (also known as semi-automated image analysis) is generally used where either the badget is constrained or where the type of subject that needs to be analysed is too difficult for an automated system to detect.  Using this type of system an image of the subject is presented on screen and the user uses drawing/measuring tools to make the measurements using a mouse.

This method is very much slower than automated methods but is always perfectly correct as long as the user can see what they want to measure.  There are several enhancements to a system like this, they include making measurements on a live image (as opposed to a captured image) and using encoded or motorised stages to allow you to make dimensional measurements of objects that are larger than a single field of view.