constrained distance between two points

hello everyone..i want to know how to find constrained distance between 2 points in an image...for eg-suppose i have an image and i want to find distance between two points such that the distance path moves over specified values of pixel(say that path should move only on white colour of image and not black)...googling this served me with bwdistgeodesic function but this works only on matlab 2011...i am using 2010 version.... in short my question is about alternative for bwdistgeodesic function.....also i want to know an alternative for imoverlay function......please help me with this.....any kind of help is highly appreciated....