该博客是由Stephan Lewandowsky撰写的，最初发布在Psychonomic Society blog.
Earlier this month,G20峰会将世界上20个最强大的国家的领导人带到德国汉堡，讨论我们全球社会面临的问题。这次会议由德国总理安吉拉·默克尔（Angela Merkel）主持，嘉宾包括唐纳德·特朗普（Donald Trump）总统和他的俄罗斯对手弗拉基米尔·普京（Vladimir Putin）。
The新政治家报道了兴奋：“当俄罗斯总统坐下来参加他期待已久的唐纳德·特朗普的会议……世界屏住呼吸。没有人能移开视线。在这张领导人的这张病毒照片中，普京的拉力没有更好的插图，固定在猛地，几乎崇拜的特朗普，土耳其总统雷克·塔伊普·埃尔多安（Recep Tayyip Erdogan）和土耳其外交部长梅夫卢特·卡维索格鲁（Mevlut Cavusoglu）中。”
这是图片：
众所周知，很难确定有多少人接触了病毒含量，但是这张照片确实吸引了很多人：搜索字符串“ Putin Picture g20病毒”返回了近一百万次命中，看来这张图片显示了图片originated with a Facebook post by a Russian journalist.
只有一个小问题：图片是假的。普京从不坐在真正属于英国总理的那个主席中。
Social media quickly caught on:
通过数字技术的进步，对图像的医生已成为可能并且容易。这似乎也很普遍，并且经常涉及那些应该更好的人，即专业摄影师。几乎在最近的世界新闻摄影比赛中，20％的决赛入围者被取消资格，因为参赛者在处理过程中不适当地增强了照片的吸引力。在2015年，世界新闻摄影比赛的一等奖获得者was stripped of the honor当发现与他的意见的违规行为时。
So how can we tell whether an image is “fake” or “doctored”? The World Press Photo judges had access to the original raw files (i.e., as they were created by the camera when the shot was taken) as well as the files submitted for evaluation, so their task was relatively easy.
但是公众呢？我们可以告诉照片是否是假的吗？我们该怎么做？据估计，每次将超过14,000,000张照片上传到Facebook小时，这个问题具有相当实际的重要性。
Arecent articlein the Psychonomic Society’s journal认知研究：原理和含义解决了这些问题。研究人员Sophie Nightingale，Kimberley Wade和Derrick Watson探索了人们一次向单一图片展示一张图像操作的能力。
The researchers studied two types of image manipulations: Implausible manipulations might involve an outdoor scene with shadows running in two different ways (implying that there was not just a single sun in the sky), whereas plausible manipulations involved things such as airbrushing (e.g., of wrinkles) and additions (e.g., inserting a boat into a river scene) or subtractions (e.g., removing parts of a building) from the picture.
The figure below shows a sample stimulus with all of the various manipulations being applied. Specifically, panel (a) shows the original. The next two panels show plausible manipulations: In panel (b) sweat on the nose, cheeks and chin, as well as wrinkles around the eyes are airbrushed out. In panel (c) two links between the columns of the tower of the suspension bridge are removed. The remaining panels involve implausible manipulations: In panel (d) the top of the bridge is sheered at an angle inconsistent with the rest of the bridge, and in panel (e) the face is flipped horizontally so that the light is on the wrong side of the face compared with lighting in the rest of the scene. The last panel, (f) contains a combination of all those manipulations.
A large sample of online participants were presented with a series of such photos. For each photo, participants were first asked “Do you think this photograph has been digitally altered?” There were three response options: (a) “Yes, and I can see exactly where the digital alteration has been made”; (b) “Yes, but I cannot see specifically what has been digitally altered”; or (c) “No.”
如果人们以一种“是”的选项做出回应，则要求他们找到操纵。再次显示了相同的照片，带有3×3的网格覆盖，并要求参与者选择包含照片的数字变化区域的盒子。
结果如下图所示。
The light gray bars show people’s detection performance, which must be compared to the horizontal dashed line representing chance performance. (Chance here is at 50% because the two yes responses are considered together as one response option.)
It is clear that people were able to detect implausible image manipulations with above-chance accuracy. Performance increases even further when all possible image manipulations are combined. However, when an image is manipulated by airbrushing, people are unable to detect this alteration. Even a subtle addition or subtraction fails to elicit strong detection performance.
The dark gray bars show people’s ability to locate the alteration provided they had indicated its presence. The location performance must be compared against the white dashed lines which indicate chance performance for each type of alteration separately. (Chance differs across manipulation type.)
毫不奇怪的是，人们无法以高度的准确性来定位喷枪的改动，因为他们首先很难检测到操纵。更令人惊讶的是，即使人们能够检测到它，也不能总是找到改变。对于回答检测问题的“是”的人来说，整体上只有45％的操作可以正确地位于图片中。
A further experiment conducted by Nightingale and colleagues largely corroborated these findings. An interesting further aspect of the results across both experiments was that the likelihood of a photo being correctly identified as manipulated was associated with the extent to which the manipulation disrupted the underlying structure of the pixels in the original image. That is, Nightingale and colleagues found a correlation between detection performance and a digital metric of the difference between the original and the manipulated versions of each picture. The manipulations that created the most change in the underlying pixel values of the photo were most likely to be correctly classified as manipulated.
乍一看，这个结果似乎完全直观。但是，结果实际上很吸引人，因为参与者从未见过相同的场景不止一次。也就是说，没有参与者看到他们显示的任何操纵照片的未经操纵版本。因此，得出的程度在多大程度上原版的photo was disrupted could be inferred from themanipulatedversion, which implies that participants were able to compare the manipulated photo with theirexpectationsabout what the scene “should” look like based on their prior experience with scenes and photos.
And when our prior experience tells us whom we would不是expect to be surrounded by other world leaders, the image manipulation jumps out in an instant:
注释