Image size with transparent background
It all depends on your needs, with a transparent background there can be completely different sizes of pictures. All Ellty template sizes are already the correct size so you don't have to worry about sizing.
Image format with transparent background
The ideal format for a picture on a transparent background is PNG, download it in the highest resolution for the best display quality.
Why do you need images with a transparent background?
Sometimes you need to apply a logo, watermark or copyright icon, easily create memorable designs using the Ellty online service.