Many modern scanners support an optical resolution of 4800 dots per inch. This works out to approximately 5 microns per pixel. Assuming a display resolution of 100 dots per inch, this represents a magnification of 48x, comparable to a low-end laboratory microscope.
These images were all scanned at this high resolution on an Epson Perfection 2450 Photo scanner in reflective document mode. Most of them have been unaltered with respect to color correction (though the automatic exposure correction was used) and were simply cropped to 1280x1024, and no other manipulation was performed (aside from automatically resizing them to 240 pixels wide to generate the thumbnails).
Feel free to use these images as desktop wallpaper, though if your screen is smaller than 1280x1024 you should crop, rather than resize, the image, to maintain the defining characteristic.