How to display images on the Page Layout ?

Using formula fields we can do this.

To add a custom formula field:

1)    Navigate to the fields area of the appropriate object

2)    Click New in the Custom Fields & Relationships section of the page.

3)    Select the data type for the formula and click next.

4)    Enter field label.

5)    Choose the Choose output type as TEXT and click Next

6)    Select the IMAGE function from the list of functions to insert an image.

7)    Provide the image URL and alt text for the function.

8)    Click Save.

Example:

IMAGE("/servlet/servlet.ImageServer?id=01530000001Rh9w&oid=00De0000000CpgS&lastMod=1311711723000", "Missed")