To return the id of the first image, use the images property in JavaScript.
Example
You can try to run the following code to return the id of the first image in a document −
<!DOCTYPE html>
<html>
<body>
<img id="image1" src="https://www.tutorialspoint.com/html5/images/html5-mini-logo.jpg">
<img id="image2" src="https://www.tutorialspoint.com/hive/images/hive-mini-logo.jpg">
<img id="image3" src="https://www.tutorialspoint.com/sas/images/sas-mini-logo.jpg">
<img id="image4" src="https://www.tutorialspoint.com/maven/images/maven-mini-logo.jpg">
<script>
var val = document.images.length;
document.write("<br>Number of images in the document: "+val);
document.write("<br>The id of the first image: "+document.images[0].id);
</script>
</body>
</html>