Change background image opacity

Question

I have a div element with text blocks and a parent div in which I have set a background image. Now I want to reduce the opacity of the background image. Please suggest how I can do that.

Thanks in advance.

EDIT:

I am looking to change the way my blog post looks at blogger.com by editing the html content. The html code looks as follows:

<div>
 //my blog post
</div>

I tried to surround the whole code above with a div element and set opacity of each div separately as below:

<div style="background-image:url("image.jpg"); opacity:0.5;">
<div style="opacity:1;">
 //my blog post
</div>
</div>

But it is not working.

Answer 1

Nowadays, it is possible to do it simply with CSS property "background-blend-mode".

<div id="content">Only one div needed</div>

div#content {
    background-image: url(my_image.png);
    background-color: rgba(255,255,255,0.6);
    background-blend-mode: lighten;
    /* You may add things like width, height, background-size... */
}

It will blend the background-color (which is white, 0.6 opacity) into the background image. Learn more here (W3S).