Relevant portion of the /etc/emulationstation/themes/simple/sega32x/theme.xml:
<image name="background" extra="true">
<path>./art/32x_art_blur.jpg</path>
</image>
Files exist:
pi@raspberrypi /etc/emulationstation/themes/simple/sega32x/art $ ls -lah
total 204K
drwxr-xr-x 2 pi pi 4.0K Jul 17 21:39 .
drwxr-xr-x 3 root root 4.0K Jul 17 21:39 ..
-rw-r--r-- 1 pi pi 156K Jul 17 21:39 32x_art_blur.jpg
-rw-r--r-- 1 pi pi 23K Jul 17 21:39 32x_art.png
-rw-r--r-- 1 pi pi 14K Jul 17 21:39 32x.svg
