Replace the question mark with the URL of an image on the Web, and replace "X" and "Y" with height and width values in pixels. When resizing images using HTML, remember that image quality degrades ...

Compressing a JPEG to a Height & Width. Digital cameras -- especially high-end digital SLR cameras -- often take images at a high resolution; an 8-megapixel camera set on the highest resolution ...

What you're looking for is probably to set width to 100%, then set max-height and max-width to the actual size of your image if you want it to never scale above that size: ...