How do i set laptop background image on my compaq 615?

This can be found in the Help and Support section of Windows on your laptop.

To change the desktop background

1. Right click on your desktop-Select personalize. This will open a window that asks you to select your desktop background
   
   

2. Click the picture or color that you want to use for your desktop background.
   

   If the picture you want to use isn't in the list of desktop background pictures, click an item in the Picture location list to see other categories, or click Browse to search for the picture on your computer. When you find the picture that you want, double-click it. It will become your desktop background.
   

   Look for pictures in other locations on your computer
   

3. Under Picture position, click the arrow and choose whether to crop the picture to fill the screen, fit the picture to the screen, stretch the picture to fit the screen, tile the picture, or center the picture on the screen, and then click Save changes.
   

• If you choose to have a fitted or centered picture as your desktop background, you can also frame your picture with a color background. Under Picture position, click Fit or Center. Click Change background color, click a color, and then click OK.
  

• To make any picture stored on your computer (or a picture you are currently viewing) your desktop background, right-click the picture, and then click Set as Desktop Background.
  

The Set as Desktop Background option

Find the image you want to use, right click on the image, and "Set As background".

Here's a nice repository from Microsoft.
http://windows.microsoft.com/en-US/windows/downloads/personalize/wallpaper-desktop-background