1.Log in your blogger account
2.Add an image in your post.
3.After adding the image go to edit HTML from your post.
4.Find the line which start from <img border=
5.Make sure it's the image that you want to use.
6.Now after finding the line add your keyword in the code in alt tag like i have done below.
7.As you can see "health tips"is my keyword that i used you can use yours just before the end of this line
/></a>
THAT'S IT SEE IT IS SO SIMPLE TO DO JUST ADD YOUR KEYWORDS IN YOUR IMAGES SO THAT SEARCH ENGINES CAN FIND YOU.