Great idea but search result images are also replaced, and scrolling is an issue - a "flicker"/moving effect as you scroll up or down. The alt text is slap over the center of the image with an opaque background so you can't properly see images - it would be more usefull lower down. Having the ability to set a minimum size for alt text would help, as would an option to display a ? Or info symbol to hover over to see alt text. I find alt text really helps me understand images, I don't need it covering the entire image like it does for icons.