In answer to your question re: white backgrounds;
You can go to lunapic.com and upload the graphic there. If it has a white background it will show as white. If it is transparent it will show as grey and white checks behind it.
If you have a white background that you want to make transparent, click the edit tab in lunapic and choose transparent at the bottom of the drop drown menu. Now click on the white area around your graphic and it will change to clear. Save to your computer. Hope that helps.