can anyone tell me in what folder the factory background images are located?

I created 600x360 pixel images and stored them in the default Images folder. While at the home screen, hit the drop down menu bar and "Set background image...". The browse button will let you go to any folder you choose to add backgrounds to the default list.

/usr/share/backgrounds/

And that size, 600x360 pixel image works well? I was just thinking about attemping to crop some photos down to something that might work. But, I have very little experience in making backgrounds like this.

I usually go for 800x480, that being the screen resolution.

Or 800x800 also works, if you do rotation. (With rotation, the background doesn't redisplay right when you rotate the screen, but if you reselect the background afterwards, it'll work.)

Linux normally can stretch or perform other methods to fill the screen. I used 600x360 because that was the size of a matrix background created specifically for the N810. I did pick stretched which would allow it to fill the screen if required.

Is there anyway with the Set Background Image prompt to either list your own backgrounds in the drop down, or when you click on browse it goes to a specific folder (instead of the default images folder)?