Default m/f Icons

I want to change the default icons when a member doesnt have a picture of the grayed out man...I have created the same size icons that i want to use and have uploaded them in template/base/images but they are not changing on my site. Anyone know where I need to put them so that I can over ride the current default icons that are there?

template/tmpl_uni/images/icons

man_big.gif
man_medium.gif
man_small.gif

woman_big.gif
woman_medium.gif
woman_small.gif

visitor_big.gif
visitor_medium.gif
visitor_small.gif