Declaring an image with explicit dimensions is only a minor extra effort in coding. To your visitor, however, it makes a lot of difference. Your web site will be looked at as being very "user-friendly", simply as "professionally designed".

Basically you could simply write down all the images and text fragments in between and leave it to the browser how to arrange them. The browser would load one after the other and carefully display what has been loaded so far. For the features still open at that time the browser can do nothing better than display some default symbols and paint the text around those symbols.

Later, when the corresponding image is loaded, the text around it will normally have to be re-arranged. If the visitor's reading has arrived somewhere in the middle of the text at that time, it will be interrupted. If the visitor is forced several times to read a paragraph over again, it will be annoying. That's exactly the opposite of what you want.

Instead, you can tell the browser right in the first place how much space should be left open for the image:

		           <IMG  ...   HEIGHT="..." WIDTH="...">

By doing so, you can enable your visitors reading your content comfortably - even though your web site is not yet loaded completely. If you do it in a clever way, your visitors will hardly notice that the loading is taking time. They will perceive it as if your web site would be "virtually instantly" loaded.