embedding background image data into css as base64, good or bad practice

Question

The other day I was looking at the source of a greasemonkey userscript and noticed the following in their css:

.even { background: #fff url(data:image/gif;base64,R0lGODlhBgASALMAAOfn5+rq6uvr6+zs7O7u7vHx8fPz8/b29vj4+P39/f///wAAAAAAAAAAAAAAAAAAACwAAAAABgASAAAIMAAVCBxIsKDBgwgTDkzAsKGAhxARSJx4oKJFAxgzFtjIkYDHjwNCigxAsiSAkygDAgA7) repeat-x bottom}

I can appreciate that a greasemonkey script would want to bundle anything it can within the source as opposed to host it on a server, that's obvious enough. But since I had not seen this technique previously, I considered its use and it seems appealing for a number of reasons:

1. It will reduce the amount of HTTP requests on page load, thus enhancing performance
2. If no CDN, then it will reduce the amount of traffic generated through cookies being sent alongside of images
3. CSS files can be cached
4. CSS files can be GZIPPED

Considering that IE6 (for instance) has problems with cache for background images, this seems like it's not the worst idea...

So, is this a good or bad practice, why WOULDN'T you use it and what tools would you use to base64 encode the images?

Answer 1

It's not a good idea when you want your images and style information to be cached separately. Also if you encode a large image or a significant number of images in to your css file it will take the browser longer to download the file leaving your site without any of the style information until the download completes. For small images that you don't intend on changing often if ever it is a fine solution.

as far as generating the base64 encoding:

• http://www.motobit.com/util/base64-decoder-encoder.asp (upload)
• http://www.greywyvern.com/code/php/binary2base64 (from link with little tutorials underneath)

Answer 2

If you reference that image just once, I don’t see a problem to embed it into your CSS file. But once you use more than one image or need to reference it multiple times in your CSS, you might consider using a single image map instead you can then crop your single images from (see CSS Sprites).