I'm trying different JPG files, but it doesn't work. Why?
Pixel Peeper reads Exif and XMP to obtain camera settings and Lightroom adjustments.
If this kind of metadata is not present in the file, you won't see any results. Many photographers choose not to include it. Some websites (e.g. Facebook and Instagram) remove all metadata from their photos.
See also: How to Find Photos with EXIF data