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First you must put both elements detritus from a div or figure with position: relative and display: inline-block;, then you can put a position: absolute; in the label or figcaption and position it with the properties top, right, bottom and/or left.
#container {
display: inline-block;
position: relative;
}
#container figcaption {
position: absolute;
top: 145px;
right: 20px;
font-size: 40px;
color: black;
text-shadow: 0px 0px 5px black;
}
<figure id="container">
<img src="http://cdn.flaticon.com/png/256/63523.png" />
<figcaption>Teste</figcaption>
</figure>
In the example below, I have the image of a gift card and want to enable the label inside the taja of the same.

I really liked the two models. Thanks for posting helped me clarify this doubt.
– Ruan Araújo