The default alignment is to the left. The optimal image tag has several things. It naturally has the name of the image, the width and height, the border size, the alignment specification, and the alternate description so people who connect to your site without graphic capabilities will get a text description. The width and height codes serve a very important purpose that will make your viewer's visit much more pleasant. These codes tell the browser exactly the size of the image.
Images take much longer to download than text.
So the browser can block out an area for the graphic, plop the image's ALT tag where the graphic will be, and get the text on the page much more quickly so you can start reading while the graphics are downloading. The easiest way to determine an image's height and width is to view it in a graphics program such as Paint Shop Pro or Adobe Photoshop. Well here's an example. There is one more important item to remember. If there is room on your page for text to load around the graphic, it will do so.