Distorted can mean a lot of different things.
By distorted, do you mean low resolution and a lot of "trash"? You either need to use a digital photograph or have the highest quality resolution scanner available. The machine will carve exactly what you give it, so a low resolution scanned photograph will give you a low resolution litho.
By distorted, do you mean stretched or skewed? You would need to make sure you use the corners to enlarge or decrease the size; not the side or top & bottom nodes.
Post a photo of the litho, so we can have a better idea of what you are talking about.
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