While JPEGs are possibly the most common digital image file type in the modern era, PNGs are also supported just about everywhere. There’s really no blatantly right or wrong choice between the two much of the time; however, they both have their advantages under specific circumstances, so it’s more a matter of efficiency.
You can use either for a photograph, but if you’re worried about file sizes, the compression you get with a JPEG is your friend. On the other hand, if you want the image to be as clear as possible, PNG is the better one to go with. Similarly, if you have some high-resolution imagery like a chart or graph that you want to transfer to a smaller screen, switching to a smaller JPEG file format and size should be no problem.
Really, the biggest deciding factor comes down to background transparencies. If your image needs to have a transparent background, JPEG is simply not a viable option because it doesn’t support them at all. So, you’ll either need to go with PNG, or try using GIF if the compression isn’t too much of an issue.
