Usually automated image processing is tough without a priori info about the image, or some human input. Adding to these methods, a 'holes' fill algorithm can b

Usually automated image processing is tough without a priori info about the image, or some human input. Adding to these methods, a 'holes' fill algorithm can be very helpful. This would proably be used in place of your Alpha Mask. The process can be run multiple times with different parameters for better results. For example, doing edge detect->threshold->edge detect (with different parameters) can help remove some of the smaller artifacts you see in the images. If you're able to have some manual input, simply clicking the object of interest or doing a rough outline can be a great addition to an algorithm, especially in avoiding the problem seen in Global Threshold with Complex Background.