Get a mask of the blue feet. Use the Color Thresholder app on the Apps tab of the tool ribbon. Then call imerode with a structuring element big enough to separate the toes. Then use bwareaopen to extract only blobs big enough to be the soles (not the toes). Then call regionprops. Something like
rgbImage = imread(fileName);
mask = createMask(rgbImage);
se = strel('disk', 5, 0);
mask = imopen(mask, se);
mask = bwareaopen(mask, 5000);
props = regionprops(mask, 'all')
You will need to adjust some parameters above. You may want to use polyfit to find out the angle of the footprint trail and rotate the image so that the steps are mostly in the vertical direction. Then rotate the mask and call regionprops again.
With the aligned/rotated mask, you will then want to look at using kmeans or thresholding to figure out which blobs are on the left and which are on the right. Then look at each foot in turn to get the distance between each sole centroid. You may have different distances for the right and left foot.
It's a generic, general purpose demo of how to threshold an image to find blobs, and then measure things about the blobs, and extract certain blobs based on their areas or diameters.
If you still need help, write back.
