limitations of CUPS command line printing of image files

I have my default printer set: lpoptions -d HP_ENVY_5530_series. I can print some text: echo HELLO > h.txt lp h.txt > [CUPS understands many different types of files directly, including text, PostScript, PDF, and image files.](http://www.cups.org/documentation.php/options.html) I can print a Portable Network Graphics: lp Gnome2.26-printing-dialogue.png. A Scalable Vector Graphics: lp Cups_simple.svg - prints as its internal text contents, which isn't much use. A scanned JPEG: lp 022.jpg - gets stopped "Unable to open image file for printing!". If I convert it to a PNG with ImageMagick - convert 022.jpg 022.png, I can then print it lp 022.png. I would like an explanation for these limitations of the CUPS lp command.