Feature detector that doesn't use corners
If you have prior knowledge of the objects expected size you should ignore interest points of too small scale. I think these objects (thanks to round shape and contrast with the background) it should be an easy task for blob detection algorithms, you'd get one detected blob / item. Note that for SIFT or SURF the major orientation isn't well defined for blobs with rotational symmetry but it might be sufficient to assume fixed orientation (like on U-SURF).