If you had done a view source on the output html you would have seen this
<img src=imagesMVC-0015.JPG>
This is because the \ character is the escape character in php, so in order to print a \ you have to escape it like this \. This means your final code should look like this:
<?php
echo "<img src=images\\\\MVC-001S.JPG>";
?>
however to make this well formed html you should do this instead:
<?php
echo "<img src=\"images\\\\MVC-001S.JPG\">";
?>