1

I've got two jpegs of the same photo of different sizes and attributes. How can I tell if one is the original taken by an iPhone4 or if neither is the original, determine which has the most information?

Adobe Bridge for the first photo shows this metadata:

enter image description here

And the second photo shows this metadata:

enter image description here

I think neither is the original since Wikipedia article on iPhone4S says the rear camera was 8 megapixels.

Here is another version of the file that is higher resolution, but doesn't match the 8 MP camera of the iPhone4S:

enter image description here

  • 1
    It's a judgement call that requires you to examine the image contents. – xiota Aug 17 at 21:07
4

You can't really tell from these data. Of course, one could hope that the bigger file holds a bit more information, but it could just be the other one badly re-encoded. Utilities such as ImageMagick's identify can tell you the JPEG "quality" setting (and the chroma sub-sampling) but you can still be looking at a re-encoding that caused some data loss.

If you have both images, you can:

  • convert them both to PNG
  • reencode the PNG to JPG with the same settings for all

The bigger file will now correspond to the initial picture with the more "information" (but, strictly speaking, this could be added noise).

  • The smaller file could just be optimized (jpegoptim - image data would be identical). Compression artifacts might not recompress efficiently (larger file worse, even with same quality setting). – xiota Aug 17 at 21:26
  • 1
    Yes, which is why decompressing & re-compressing with known settings is the only way to tell. Compression artifacts are due to information loss, they are the reason why the re-compressed file is smaller. – xenoid Aug 17 at 21:47
  • 3
    Because this is not noise, this is correlated noise, within the 8x8 encoding blocks whose positions never change. If you were to shift the image a couple of pixels, then the 8x8 blocks boundaries would be different, there would be little/no correlation within the blocks and re-encoding could yield a bigger file. try for yourself, you'll be surprised. – xenoid Aug 17 at 22:40
3

It's unlikely that any of the images you have is the original if you do not have access to the device that they came from. Apple devices typically resize images when sharing. If you need the original, contact the owner of the device that created them.

Deciding which image is "closer" to original is a judgement call that requires you to examine the image contents, but the third file is probably "closer" because:

  • It has a higher resolution than the other two files.
  • It came from an email, presumably from someone who does have access to the original. Apple devices often resize images when sharing.

Between the first two images, the second is likely "closer" to the original because:

  • Software rarely automatically names files according to faces recognized within the image. The second file has the typical prefix-date naming scheme.
  • Display P3 vs sRGB. The first file has gone through at least one conversion pass to change colorspace.
  • Modified timestamp of first file is ~8 min after the second one.

The filename of the third image looks typical of a hash (string of numbers and letters A-F). This is typical of images that have passed through an online service, like Facebook.

  • Does the added third file's filename better suggest it being an original? (Note the timestamps just reflect time of downloading from an email attachment.) – WilliamKF Aug 18 at 19:19
  • The third filename better supports that the file has gone through an image sharing service, like facebook, because it has a filename that looks like a hash. However, it has a higher resolution and came from an "email", possibly from the owner of the "original" file, so would likely be "closer" to the original than the other two. – xiota Aug 18 at 22:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.