PHP：想象在附加图像之间添加空间？

I'm using imagick to append some images to a background image. this works fine... but the the appended images are sticking together..

is there anyway to put a space between them at all?

This is my code:

exec("/usr/bin/convert H.png E.png L.png L.png O.png +append append_row.gif");

Any help would be appreciated.