It's your compression rate. That's clear from you file size. The dpi is ok, however, I always highly recommend that people scan their chips to an exact square size. That way, if you're placing it into a formed square m(which is common on websites and thumbnail placements) it doesn't force a skewing. Yours is 416 x 419. Make it square like. If you want 250 dpi, you can make it 400 x 400, which make a great size. Go for a file size around 30k-40k for this dimension.

If you are going to stay with a larger dpi such as 250, then adjust your compression to so that your quality is higher, and which of course will also result in a larger file size.