is_page doesn't work

I’m trying to have an image change in my header.php on the blog page.
I got this. I looked at other topics as well and I’m pretty certain this is correct however it only shows the image in the else never the first image.

<?php
if ( is_page( 'blog' ) ) {
echo '<img src="link1" alt="alt-text">';
} else {
echo '<img src="link2" alt="alt-text">';
}
?>

What am I doing wrong? Why isn’t it working?