When importing objects into Blender, you need to be aware of a) which axis is up (y or z, usually — Blender uses z) and b) what world units you’re using. Blender defaults to “Blender Units”, but can easily be switched to either Imperial (inches & feet, etc.) or Metric (centimeters & meters, etc.). To do so, go to the scene panel >> units section and select whichever units you prefer to use there.
If that doesn’t work, you may simply need to rescale the image and then use ctrl/cmd+A to reset the scale.
And if that doesn’t work… then there’s a trick to it I haven’t come across, yet.
