Which tool is best for making wallpaper or background images for app

Hi,
As i am doing gui development for my app.and in this i m finding diffficulties in making background images.
Can you please suggest the tool which ia best for making the images.

Wallpaper Maker DIY is the best image creator app for iphone.

leomaster is the best tool ever

According to my opinion, Canva is the best ever app for making wallpaper or background images

As you are doing GUI Development, so according to my experience I prefer Walloid for best image maker, I hope this will help you.