http://davidbcalhoun.com/2011/when-to-base64-encode-images-and-when-not-to/
http://clagnut.com/sandbox/imagetest
http://courseware.codeschool.com/css_cross_country/slides/CodeSchool-CSSCrossCountry.pdf
https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Positioning/Understanding_z_index