符合最新标准的刑事数码照片后期处理技术

Adaptability of Forensic Digital Image Processing Techniques to the New National Standard

目的 2012年,国家颁布了《法庭科学数字影像技术规则》对现场数码照片进行标准化规范,同时对数码照片的后期处理提出了具体要求。新标准规定了"无本质变化"和"重复实现"两个限制性条款,本文按此两条款对标准设立前的刑事照片处理方法作验证,以研判这些方法是否能在新标准下继续使用。方法选4张原始图片,进行图片旋转和合并的处理操作。将处理后图片和其原始图片作对比,评判是否有"本质变化"发生和"重复实现"。结果在任何非90°及其倍数的图像旋转中,图像发生了轻微但累积性的"本质变化";合并图片的操作也难以完全"重复实现"。结论根据新标准,结合本研究得出图片进行90°及其整数倍数的旋转操作仍然适用,而非90°及其倍数的旋转以及合并图片的操作可能不再适用。

ObjectiveA new national criterion, the technical standard of forensic digital image, was issued in 2012 to regulate the manipulations of forensic digital photography in China. Since there were many methods for digital image processing before, thus, whether these methods can still meet the new standard becomes an urgent problem. Two criteria for forensic digital image processing were proposed in the new standard, “no fundamental alteration” and the “repeatable”. Here two existing processing manipulations were veriifed on whether they are in accordance with the new standard.MethodsFour original photos were selected to receive rotating and coalescing processing. Through comparison of such processed photo with its original one, whether the manipulation is of “fundamental alteration” and “repeatable” was evaluated.ResultsThe rotation by any degrees of neither 90o nor its multiples can indeed generate “fundamentat alteration”, albeit slight yet accumulative. As for the “repeatable”, the coalescing manipulation cannot be repeated in the exactly same way, either.Conclusion According to the new standard, the image rotation by any degrees of neither 90o nor its multiples becomes inappropriate. However, the rotation of both 90o and its multiples is still adaptable. Nevertheless, the images coalescing is not ever recommended since it cannot be really “repeated” exactly the same way.