That's the point.
Huh?
How did the forger, 2000 years ago, create a negative image of a man, without pigment? And how did he also know how to create a grayscale, topographic map that reveals a 3D image when analyzed with sophisticated terrain-mapping equipment?
Either the "forger" was more intelligent than the combined minds of the world's greatest scientists, or the shroud was created supernaturally.
Which position requires more "faith"?
Some people don't believe because believing would cramp their lifestyle, if you know what I mean. Would that be true in your case?
That it was created supernaturally, I'd say ;-D