This effect is called a MouseOver. JavaScript is used to swap images when the mouse passes over a specific image or link A script is placed inside the document HEAD tag. The script is called from the body of the document whenever a mouseover effect is desired. The script may be written to apply to either images or to style sheet properties. Prior to that, it was an unofficial tag. .
Accessibility is one consideration.
Frames are not interpreted properly by all browsers. Often authors forget or don't know how to break the frames when visitors leave their site. Hardly anyone enjoys surfing within another sites frames. All links need to specify a target. Multiple, sometimes useless, scroll bars can also be an annoyance to many.