Problem solved: A reliable, deterministic method for JPEG fragmentation point detection

Abstract

Recovery of deleted JPEG files is severely hindered by fragmentation. Current state-of-the-art JPEG file recovery methods rely on content-based approaches. That is, they consider whether a sequence of bytes translates into a consistent picture based on its visual representation, treating fragmentation indirectly, with varying results. In contrast, in this paper, we focus on identifying fragmentation points on bit-level, that is, identifying whether a candidate next block of bytes is a valid extension of the current JPEG. Concretely, we extend, implement and exhaustively test a novel deterministic algorithm for finding fragmentation points in JPEGs. Even in the worst case scenario, our implementation finds over 99.4 % of fragmentation points within 4 kB – i.e., within the standard block size on NTFS and exFAT file systems. As such, we consider the problem of detecting JPEG fragmentation points solved.