The first photo below is a png. It is of a good quality. It's size is relatively large -- 762 KB (only bitmap or bmp was larger).
The picture below is jpg or jpeg. It is the most common on the web. It is considered a "lossy" format where some quality is lost. The image was saved at 100% and it's size is 414 KB.
Below, you will find a gif image. It is not stored as RGB, but rather colors indexed to a palette. It is compact in size at 256 KB, but it's quality suffers a bit compared to png, 100% jpg and png.
The last pic is a bitmap. It has the largest size of all of the formats at 1,370 KB.
So if you are worried about disk space, you would want to save your pictures in the jpeg or gif formats.
Incidentally, the flower is a tropical one. I don't know the name, but I took the photograph in Nassau, the Bahamas.