1. White (or plain single color) background
2. Spread the material out so that each grain is seen separated from the rest
3. Keep a scale in the frame to make sure we can get the size scale of the photo
4. Enable the feature of the camera so that the date is printed on the photo in some place
5. Set the camera to a medium / high resolution; low resolution images are not very useful
6. Make sure the camera is focused on the grains and not on the scale or the background
Here’s an example of a photo of a sample …
The Millet Foundation 