The beauty of Lightroom is, among other things, its non-destructive image edits. The secret of those edits is the XMP file–essentially a written list of instructions that tells Lightroom how to process an image. Put another way, that XMP file contains your processing recipe: all your slider tweaks and settings to achieve the look you desire.
Every time you process a RAW image and export it as a JPEG in Lightroom, those XMP instructions can be embedded in the JPEG’s EXIF metadata, unless you select the option to strip this data from your file when exporting.
Now, developer Piotr Chmolowski has created a web app called Pixel Peeper that can read that those Lightroom editing instructions off of a JPEG image, allowing you to peak under the hood to see how a given image was edited. You simply drag-and-drop an image into Pixel Peeper and you’ll be presented with both standard EXIF data (camera model, lens, aperture, etc.) plus a sidebar with all of Lightroom’s processing tools set to where they were when the image was burned into a JPEG.
As Jayphen Simpson points out, once an image has been placed into the Pixel Peeper app, you can also save the editing information as a Lightroom preset by appending “.lrtemplate” to the end of the URL.
Again, Pixel Peeper only works if the image was processed in Lightroom and the metadata was left in tact. It will read EXIF data from images not processed in Lightroom, but won’t show any editing information.
According to the app, no images are saved to Pixel Peeper’s servers but metadata, file names and file sizes are uploaded to the apps’ servers.