Look at my color segmentation demos http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862
For this image, the background is neutral and the subject is not. So I'd probably convert to hsv with rgb2hsv() and then threshold on saturation to get highly saturated pixels. The background won't get selected. Then get rid of any small regions with bwareaopen, call regionprops, get the bounding box, and call imcrop(). The essential lines are few:
hsv=rgb2hsv(rgbImage);
s = hsv(:,:,2);
foreground = s > 0.2; % Or whatever.
foreground = bwareaopen(foreground, 1000); % or whatever.
labeledImage = bwlabel(foreground);
measurements = regionprops(labeledImage, 'BoundingBox');
bb = measurements.BoundingBox;
croppedImage = imcrop(rgbImage, bb);
or something like that. I didn't test it - that's just off the top of my head.
