I hope you can help. I have jpeg images without EXIF headers. When I use Exiftool to change the dpi (exiftool -Xresolution=300 -Yresolution=300 *.jpg) to 300dpi, Exiftool creates an exif header with this information. When I submit these images to photo libraries, they do not recognize the exif header, and uses the the dpi embedded in the jpeg-header. The problem is that Exiftool changes the previous dpi to 300, but only for images that had a pevious dpi value. Some of my images does not have a dpi value embedded in the jpeg header, and for these images Exiftool does not change the dpi to 300. When I open these images in Irvanview after using exiftool, it still shows no value for the dpi. Should I use exiftool in another way for these images?