background-image url responsive image - html

Question

I want to insert an image by CSS because I want to use captions over my image.
What I want is that the image shows completely and is responsive.
Can anyone help me with this?
Here you can see my HTML im using bootstrap. As you can see i want to let contentblock1 show an responsive image by using the CSS background-image code. I also want this background image to be responsive. But whatever i try it won't show me the background.
<div class="container">
<div class="col-sm-6">
<h1> Dit is een bootstrap site</h1>
<button type="button">click me!</button>
</div>
<div class="col-sm-6">
<div class="contentblock1">
</div>
</div>
I'm using the following CSS
.contentblock1 {
background-image: url('http://1.bp.blogspot.com/_zxdOSKs0ASI/TDMqbnatRwI/AAAAAAAAAkM/nB-DxcVcqqk/s1600/Testbeeld.jpg');
background-size: 100% 100%;
width: 100%;
}

Answer 1

width: 100px; /*you width*/
height: 100px; /*you height*/
/* optional: background-color: white; */
background-image: url('image.png');
background-repeat: none;
background-size: 100% 100%;
/*or
background-size: cover;
background-position: 50% 50%;*/
background-attachment: fixed;

Answer 2

#some-div {
background-image: <imgurl>;
background-repeat: none; //Unless you want something else
backgorund-size: 100% 100%;
}
and for responsiveness, use media-queries or a lib that is made for responsiveness such as Bootstrap.
Below you have an example of media-queries.
#media (min-width: 1200px)
{
#some-div {
width: 600px;
}
}
#media (max-width: 768px)
{
#some-div {
width: 100%;
}
}
EDIT:
http://jsfiddle.net/e8xLf4u3/
Here is your working example, it only needed content. Also, in the future please show some code for faster help and better understanding
Graag gedaan ;)