Yikes! The DPI setting in import-bmp controls something much more important than the scaled image size: It controls the size of the “pixels” that your image is drawn with, which in turn affects the end file size and could have consequences for manufacturability.
600DPI equates to 1.6 mil lines. If you’re putting this in a silkscreen layer, well, chances are, the fab’s silkscreen printer is basically 200DPI. Your image may or may not show up, depending on the fab’s pre-processing process. This goes similarly with the soldermask layer (though the resolution is often higher).
The worst is if you try to put this on a copper layer. Each 1.6mil pixel is going to throw a “trace too small” warning in the fab’s DRC software.
The moral: Be nice to your fab, and scale the image outside of import-bmp, so it processes well at 200DPI or smaller.
