Google Map Infowindow not showing properly

The issue is forced by this format inside style.css:

img {
    height: auto;
    max-width: 100%;/* <--the problem occurs here*/
}

Add this to the end of your style.css to apply the default-value for images inside the map:

#map_canvas img{max-width:none}

The issue can be you are using img{ max-width: 100%; } as universal.

Try this one in to your css

.gmnoprint img {
    max-width: none; 
}