Object detection, Kinect Depth images

Hi. I've been working with OpenCV for a while now. Both native OpenCV (C++) and emgu (C#) I want to recognize one or more "objects" in an image. This time it's a depth image from a kinect sensor. If you look at the image you can recognize 3 equal objects. I've marked it with a red rectangle.  Have never found a good object detection algorithm for my work though. I've tested edge detection:  Also tried some 2DFeatures like SURF, SIFT and FAST. They seems to work better on high contrast, high resolution objects?  Maybe OpenCV isn't that good in detect this type of objects in the scene? We are now using Matrox Image Library for this kind of detection.