Drop shadow for PNG image in CSS

Question

A little late to the party, but yes, it is totally possible to create "true" dynamic drop shadows around alpha masked PNGs, using a combination of dropshadow-filter (for Webkit), SVG (for Firefox) and DX filters for IE.

.shadowed {
    -webkit-filter: drop-shadow(12px 12px 25px rgba(0,0,0,0.5));
    filter: url(#drop-shadow);
    -ms-filter: "progid:DXImageTransform.Microsoft.Dropshadow(OffX=12, OffY=12, Color='#444')";
    filter: "progid:DXImageTransform.Microsoft.Dropshadow(OffX=12, OffY=12, Color='#444')";
}

<!-- HTML elements here -->

<svg height="0" xmlns="http://www.w3.org/2000/svg">
    <filter id="drop-shadow">
        <feGaussianBlur in="SourceAlpha" stdDeviation="4"/>
        <feOffset dx="12" dy="12" result="offsetblur"/>
        <feFlood flood-color="rgba(0,0,0,0.5)"/>
        <feComposite in2="offsetblur" operator="in"/>
        <feMerge>
            <feMergeNode/>
            <feMergeNode in="SourceGraphic"/>
        </feMerge>
    </filter>
</svg>

Some comparisons between true drop-shadow and box-shadow and an article on the technique I've just described.

I hope this helps!

Yes, it is possible using filter: dropShadow(x y blur? spread? color?), either in CSS or inline:

img {
  width: 150px;
  -webkit-filter: drop-shadow(5px 5px 5px #222);
  filter: drop-shadow(5px 5px 5px #222);
}

<img src="https://cdn.freebiesupply.com/logos/large/2x/stackoverflow-com-logo-png-transparent.png">

<img src="https://cdn.freebiesupply.com/logos/large/2x/stackoverflow-com-logo-png-transparent.png" style="-webkit-filter: drop-shadow(5px 5px 5px #222); filter: drop-shadow(5px 5px 5px #222);">

img {
  -webkit-filter: drop-shadow(5px 5px 5px #222222);
  filter: drop-shadow(5px 5px 5px #222222);
}

That worked great for me. One thing to note tho in IE you need the full color (#222222) three characters don't work.

If you have >100 images that you want to have drop shadows for, I would suggest using the command-line program ImageMagick. With this, you can apply shaped drop shadows to 100 images just by typing one command! For example:

for i in "*.png"; do convert $i '(' +clone -background black -shadow 80x3+3+3 ')' +swap -background none -layers merge +repage "shadow/$i"; done

The above (shell) command takes each .png file in the current directory, applies a drop shadow, and saves the result in the shadow/ directory. If you don't like the drop shadows generated, you can tweak the parameters a lot; start by looking at the documentation for shadows, and the general usage instructions have a lot of cool examples of things that can be done to images.

If you change your mind in the future about the look of the drop shadows - it's just one command to generate new images with different parameters :-)