Targets that are not perfectly flat can cause problems in accurate reconstruction of the bird's eye view of the target image. This can be caused either by the athlete not hanging the target flat on the target holder causing a "bubble" in the paper. Or, if the target was stored rolled up, this too could cause a "bubble".
The camera will pick up on these Z-axis distortions. Because the target is expected to be flat, and it isn't, this will cause the aiming bulls to appear stretched or shrunk unevenly.
Ensure the target is perfectly flat before taking a photograph of it. This may require clips or weights at the edge of the target to keep it flat.