Questions and postings pertaining to the development of ImageMagick, feature enhancements, and ImageMagick internals. ImageMagick source code and algorithms are discussed here. Usage questions which are too arcane for the normal user list should also be posted here.
GrabCut might succeed without a user-supplied mask, but I doubt it for this image. The top half is fairly easy, but not the bottom half, especially around the left foot.
Grabcut and Clipping magick may help, but I suspect you will need to manually edit it. Clipping Magick allows you to quickly draw around the object and have it remove the background. But for complex backgrounds you need to draw it multiple places to get all the background remove. But you still may have to manually edit it with very complex backgrounds. Photoshop and Gimp have elastic outline tools that may help.