By default, a browser will ignore background css rules when printing a page, and you can't overcome this using css.
The user will need to change their browser settings.
Therefore, any image which you need to print should be rendered as an inline image rather than a css background. You can use css to display the inline image only for print though. Something like this.
HTML
<div class"graph-image graph-7">
<img src="graph-7.jpg" alt="Graph Description" />
</div>
CSS
.graph-7{background: url(../img/graphs/graph-7.jpg) no-repeat;}
.graph-image img{display: none;}
@media print{
.graph-image img{display:inline;}
}
Using this code, or similar code, means the image is used once in html and once in css.
The html version is hidden using css, and for print it displays as normal. This is a hack, but it will do what you want it to do. It will print the image.
Having said that, what you're doing is terribly bad practice. Nothing which conveys meaningful information to the user should be conveyed using css alone. Not only is it semantically incorrect, but it makes the graph less useful to users. An inline image is much better, and if you can, that's what you should use.
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