Take a look at the JS Fiddle provided below, it should clarify things. Right now, I have applied a negative margin to the image causing it to overlap the entire red block. What I'm actually aiming for is to have the image overlap only the red background but not the content (text).
.coloredBlock {
background-color: red;
color: white;
text-align: right;
}
.imageBlock img {
margin-left: -120px;
}
<div class="container">
<div class="col-md-6 coloredBlock">
<h1>This is some text</h1>
</div>
<div class="col-md-6 imageBlock">
<img src="https://www.w3schools.com/w3css/img_fjords.jpg" alt="">
</div>
</div>