Is there a way to style the alt? With javascript? With pseudo attributes? like this:
This is the caption&l
It's the alt attribute, not tag, and it's not possible to style it directly. It's simply a piece of text that is displayed if the image fails to load. You can style the element though and it will affect the styling of the alternative text in most browsers (though not IE).
If you were referring to the tooltip that appears in some browsers when you hover over an image, that's achieved with the title attribute and works on all elements, not just images. The alt attribute is also used by IE for this purpose on images, but this is not standard. Either way, title tooltips cannot be styled. If you need fancier tooltips, you'll have to create your own. I imagine there's a plethora of such things out there.