This post is about a small, technical tool that should be in everyone's skeptical toolkit. It finds its place in a wide variety of claims that have almost anything to do with images as the source of that claim.
For example, back in the day, proponents of the Apollo "Moon Hoax" had a lot of different claims they could make. They were wrong, but they could still make them. One of the three or four predominant claims made was, "Why hasn't NASA (or another space agency) taken any photos of the landing sites?" The explanation gets to the limits of physics and optics - something a first-year physics student (or even high school student) could explain, but one that defied most hoax proponents.
The question amongst us astronomically minded skeptics was, "How will the hoax proponents respond?" We didn't have long to wait: "They're Photoshopped!" (such as this website, and the embedded YouTube video). And, to a casual observer, the hoax proponents seemed to maybe have a point. After all, if one were to examine the metadata of the images of the landing sites posted online, it said that they were created in Photoshop.
This claim is repeated all over the internet with claims of faking other images, and the generic form is this: “If you look at the metadata for the image, it says that it was created or modified in [insert any image processing software name] and therefore that is PROOF POSITIVE that the image has been faked."
People who make that claim are wrong.
So then, what is metadata? Back in the pre-digital era, photographers kept log books that carefully documented all of their settings, like shutter speed or aperture. Metadata is the digital equivalent of this, and it is usually stored inside of the image file (commonly JPG) itself. When I take a photograph with my camera and then look at the metadata, the metadata will tell me the camera type and model, the firmware version, the shutter speed, f-stop, ISO, any mode I had the camera on, any color adjustment, and lots of other information. If you’ve ever geotagged a photo, that’s also put into the metadata.
Many computer-based photo storage solutions like Apple’s iPhoto will write metadata into the image file itself when you tag images with keywords or faces.
So, metadata is the digital equivalent of a logbook, and it is created automatically and stored within the image itself. It's very useful. It’s not a bad thing, and for a guy like me who documents stuff like crazy, it’s a good way to keep track of things.
But, metadata doesn't just happen in the camera or in digital photo storage software. It will also be written by most software that does anything with photos, such as Adobe's Photoshop software. After all, from a marketing standpoint, it, too, wants to let anyone looking at the metadata know that that software had some role in the image you’re looking at.
That role could be as simple as saving a photo as a different file format. I’ve often taken image files that were saved in one file format by graphing software I use, opened them in Photoshop, and saved the graph as a different file format. I did absolutely no manipulation to the image in Photoshop, but Photoshop will <em>still</em> write into the metadata that I have done something to that image in Photoshop; it will even include the version of Photoshop that I used.
Or, I have panorama-stitching software that will also write out metadata stating that it created the image, which I then take into Photoshop and may adjust the brightness and Photoshop will again overwrite that panorama software's tag with its own.
That's my photography, and some of my work images for publication.
Similarly, I have taken spacecraft images, and not liking the more common tools that many in my field use to create a mosaic, I will do it in Photoshop. That means taking perfectly good, normal images, placing them carefully relative to each other, and then saving the final mosaic as a single file.
That doesn’t mean I faked it. That doesn’t mean I manipulated it beyond just stitching the mosaic together. That doesn’t mean I brushed over some alien who was waving a spotlight at me, nor does it mean I drew in a lander and astronaut foot trails over what had been smooth terrain. All it means is that Photoshop happened to be the last piece of software that saved the image.
It's incredibly benign. It's something that most of us do every day without paying it a second thought. It's something that millions of copies of image software do every day without people knowing. And because of this, if a conspiracy-minded person feels like it, they can look at the image file's metadata, pull out the line that says "Adobe Photoshop," and then to most people it will seem to cast doubt on the image.
It takes just a few seconds to claim it’s a conspiracy, but I’ve now spent a few hundred words explaining why it’s not. You may not run across this claim often, but when you do, you'll be better able to understand why it's not a vast conspiracy.