public int getPhysicalWidthDpi() {
        return physicalWidthDpi;
    }
Returns vertical dpi of the image, if available.

<p>
Applies to TIFF (optional), BMP (always), GIF (constant: 72), Jpeg (optional), PNG (optional), PNM (constant: 72), PSD/Photoshop (constant: 72).
</p>

@return -1 if not present.
src/main/java/org/apache/commons/imaging/ImageInfo.java