1. A method for aligning image data printed on a receiver medium using two printheads in a multi-printhead printer, comprising: printing a test pattern including a plurality of features on the receiver medium using first and second printheads as the receiver medium is moved relative to the printheads in an in-track direction, wherein some of the features in the test pattern are printed with the first printhead and some of the features in the test pattern are printed with the second printhead, wherein the features in the test pattern are separated by predefined test pattern feature separations; capturing a digital image of the printed test pattern on the receiver medium using a digital image capture device; analyzing the captured digital image to determine a first camera pixel separation between two features printed with the first printhead; determining a camera scale factor responsive to the determined first camera pixel separation and the corresponding test pattern feature separation; analyzing the captured digital image to determine a second camera pixel separation between a feature printed with the first printhead and a feature printed with the second printhead; using the determined camera scale factor to scale the second camera pixel separation; comparing the scaled second camera pixel separation to the corresponding predefined test pattern feature separation to determine an alignment error; and using the determined alignment error to adjust the alignment of the image data printed with at least one of the first and second printheads.