Quality Assessment for Reassembled Image Files

Reassembling fragmented image files plays a crucial role in seizing digital evidence from scattered digital image files. However, little attention has been paid to the quality assessment for reassembled image files. We propose a method to assign a reassembled image file with a score indicating its quality, defined as the amount of information that the reassembled image affords for its original image. The score ranges from 0 to 1. A higher score indicates better quality. The basic idea of the proposed method is to disintegrate the quality assessment of a reassembled image file into the calculations of the contributions of the fragments contained in the reassembled image file. For each fragment, if it is not from the original image file, it affords the least contribution. Otherwise its contribution depends on the extent to which the fragment and its neighbor fragments are concatenated correctly. We validate the performance of the proposed method with an extensive subjective study involving 588 reassembled image files. We also show that the existing quality assessments for images cannot be directly used to assess the quality of reassembled image files.