As an input I have a photo of a simple symbol, e.g.: https://www.dropbox.com/s/nrmsvfd0le0bkke/symbol.jpg

I would like to detect the straight lines in it, like points of start and ends of the lines. In this case, assuming the top left of the symbol is (0,0), the lines would be defined like this:

start end (coordinates of beginning and end of a line)
1. (0,0); (0,10) (vertical line)
2. (0,10); (15, 15)
3. (15,15); (0, 20)
4. (0,20); (0,30)

How can I do it (pereferably using OpenCV)? I though about Hough lines, but they seem to be good for perfect thin straight lines, which is not the case in a drawing. I'll probably work on binarized image, too.