Though 600 dpi is good enough to scan photos, for some of my coins which measured few millimeters, this is not enough.
From the specification of MP287, it is clear that it supports 1200 x 2400 dpi. So, I should be able to scan at 1200 dpi. After searching a lot, I found the answer.
The 1200 dpi option will be available only from the scan dialog of the driver - ScanGear.