404 for images

throws 404 code and delays page load

/wp-content/themes/edu-clean/_inc/css/images/list.gif
/wp-content/themes/edu-clean/_inc/css/images/list-alt.gif
/wp-content/themes/edu-clean/_inc/images/nivo/bullets.png
/wp-content/themes/edu-clean/_inc/images/nivo/arrows.png