Tile up your background
In PowerPoint, you can tile up your background so that you will see repeated images filling up your slides. This may look tricky, because there isn't an option where you can choose to tile or stretch your background. So how can this be done?
First, click Format > Background.
Click on the dropdown field and select Fill Effects.
This will bring up the Fill Effects dialog box.
Select the texture tab.
Click on "Other Texture...".
Look for the image you want for tiling the background.
Click Ok and Apply to All.
Now, you will see repeated image filling up the slides.