There is a new command in Lightroom 5 that will verify the integrity of any Adobe created DNG files (Library>Validate DNG Files). If it finds any invalid DNG files, they will automatically be placed in a special collection.
This validation is helpful when we want to check to make sure that files haven’t been corrupted after copying then from one drive to another. It can also be helpful if we want to know with certainty if anything has changed in the original source image. If something has changed, then we know that something has gone wrong and it can (hopefully) be solved before more damage is done (like additional files are copied or changed).
It’s important to note that the data that Lightroom is verifying is the “original source image” – which, in a DNG file is never supposed to change. Lightroom is checking this information independently of the other information (that may have changed) in the file.
Here is a little more detail (and please understand that this is a bit of an oversimplification): the DNG file contains many different “kinds” of information. It’s helpful to imagine that the DNG file is really more like a file cabinet and each different “kind” of information is stored in a different folder in that cabinet. This enables certain segments of the file (one folder) to be altered independently of another segment (or folder).
For example, if you add IPTC data to a DNG file (by adding keywords, copyright etc.), the data in the IPTC folder changes, but the source image data (which is stored in another folder), remains unchanged. Even when you make edits to a DNG file in Lightroom’s Develop module (or Photoshop’s Camera Raw plug-in), all of the changes are made to the DNG file (as a set of instructions) and are stored in a separate folder so as not to change the original source image data. It’s then up to the software – PS or LR to take the original source data and then apply the set of instructions (from the other folder) and display the results on screen so that it “appears” as if the changes have been made when, in fact, the original source information has not been touched. Of course the benefit of not touching the original is that the entire workflow is then non-destructive: the changes can be modified or removed at any time without changing the original source data.
Here we can see that there are many types of data in a DNG file that can be changed including EXIF, IPTC, AUX, RDF etc.). However, the Source Image Data should remain unchanged – and that is what the DNG verification feature validates.
So, it’s the best of both worlds, you can now validate an Adobe DNG file to confirm that the source image data has not changed, yet still make changes to other information in the file in order to add metadata and enhance the image.
Note: Only DNG files created by Adobe software can be validated (camera-‐created DNGs cannot be validated because they do not contain the necessary checksum).
For more information, be sure to check out Peter Krogh’s in depth explanation.