6.Image Optimization (SEO on page)
There are 3 key parts in a image where you can save the space : bit depth (number of colors), dimension and resolution. Here is a show for you about the practicalities of web graphics optimization, and some bit of the technicalities. You do not need expensive graphics editors to compress the sizes of your images, as there are plenty of free utilities and shareware that will do the job for you.
If we think why we use image in a page then I will say images are the best representative for a place ,things ,human beings but web crawler will not detect the images it count text only.
Another reason is that all browsers will not show all types of image then only user will see text used in image.
For optimization we use following in a image
1. Name of image in title tag(it is optional)
2. Name of image in alt tag
Example
<img src="URL/location of image" width="336" height="93" alt="name of image">