max-width:100% on all images from the off can be a bad idea.max-width:100% style declaration to all images when building a responsive site. Here's one reason why it might not always be a good idea.divdivCheck in IE8, it seems the image above disappears.
So (in IE8) if you set max-width: 100% on all images and an image happens to have a floated parent that doesn't have a specified width, the max-width is interpreted as 0 because the parent is collapsed.