The default is left. If you simply place an image command on a page, the image will pop up hard left. Images usually don't stand alone. They often have text along side of them. So, remember that during this part of the lesson, numbers refer to pixels rather than inches, or centimeters.
Every image is made up of pixels.
This means that you can also denote an image by the number of pixels. I have an expensive graphics program that tells me so. You might also want to open the image by itself in your browser window. When the picture pops up, look at the title bar along the very top. Some browsers display the pixels there for you.