Why does Opera 9 have a space between these two images?

Answer 1

If it's the issue I think it is, it should be fixed if you add this CSS:

img {
    vertical-align: top
}

Or this:

img {
    display: block
}

Answer 2

Try removing the whitespace between the first </div> and the second <div>. Sometimes these CRLF whitespace characters are interpreted by the browser as an indication of physical space.