when you put a banner on a shield it is inverted/messed up and doesn't look good

I wanted to combine a banner that I got from a command and put it on a shield.

I went on planet minecraft and got the copy code for a banner (it was a pic of a pug) and used it in minecraft. The command worked but when I put it on a shield it looked like a bunch of random pixles that made up the original banner but put randomly on it. I tried with another banner, same thing.

Get a banner that is complex. Put it on a shield.