I'm writing a program that can detect veins(the dark lines) on an arm.
When looking at the image at full size, you can easily make out where they are.
But when zoomed in around a vein I get something ambiguous which doesn't seem to have edges anymore.
I've tried edge detection but it doesn't work well since the apparent 'edges' aren't actually edges when viewed close up.
Took me a while to learn all the necessary mathematics, but I've managed to write a ridge detection algorithm as suggested by Rethunk. This question helped alot.
Still needs improvement though, probably using scale space image processing as suggested by Fat32.