I always forget that I have a custom background for my Google homepage. The thing that gets me every time is that I'll go to Google then wait a second to type something in. All of a sudden I get this picture that fades in like a nightmare (that one on the left).

Here's where that picture is from:

Anyway, if you'd like to add your own custom background to your Google homepage, follow these instructions

1. Sign in to your Google Account in the top right corner of the Google homepage.

2. Click Change background image in the bottom left corner of the Google homepage.

3. Choose where to select your background image

4. Once you've chosen your image, click Select at the bottom of the window. It may take a moment before your new Google homepage background appears.

You can remove your background image at any time by clicking Remove background image in the bottom left corner of the homepage.

Source: http://www.google.com/support/websearch/bin/answer.py?hl=en&answer=180720