Want to include a picture on your spreadsheet? It's quick and easy. Go to the 'Insert' tab, and you'll see the third button from the left is 'Picture'. If you click it, you can browse through the folders on your computer until you find the picture you'd like to include. Click 'Insert', and you'll find the image sitting in whichever worksheet you're currently working on. You can resize it and move it around just like any other object until it's positioned as you'd like.
Alternatively, you can copy and paste pictures from other sources - like the Internet, or another file.