You can use the Bias tool to correct distortions in the aspect ratio of an image.
Normally, this ratio is maintained when scaling an image in AutoCAD. However, if the image is distorted due to paper shrinkage or optical distortions in the scanning process, the Bias tool can correct the aspect ratio by resizing the image in one or two dimensions, using either existing vector geometry or a distance you specify.
When you use the Bias tool, AutoCAD Raster Design toolset prompts you to enter calibration (existing) distances and desired distances in the X and Y directions. The application stretches or shrinks the entire image to correspond to the ratio of the distances you specified. The X and Y directions are relative to the image and not its position in the drawing. In each case, you can select two points (or enter a distance) to specify the calibration distance, then select two corresponding points (or enter a new distance) to specify the desired distance. You can also use existing geometry to define the desired distance; for instance, by selecting the endpoints of a line.
AutoCAD Raster Design toolset maintains the current base point location for the image unless you specify a new base point. You can enter a new base point with numeric values or by clicking the point in the image.