How to display pictures from database?

You’ll want to use wp_get_attachment_image_url() or wp_get_attachment_image(). You just pass them the ID of the image in the database and the size you want.

wp_get_attachment_image_url() gives you the URL of the image:

echo wp_get_attachment_image_url( $attachment_id, 'large' );
// http://example.com/wp-content/uploads/2017/01/image-1024x1024.jpg

While wp_get_attachment_image() gives you a full image tag:

echo wp_get_attachment_image( $attachment_id, 'large', false, [ 'class' => 'my-image' ]  );
// <img src="http://example.com/wp-content/uploads/2017/01/image-1024x1024.jpg" class="my-image" etc...

If you do want it from your theme folder, then a better method these days is get_theme_file_uri(), because it supports being filtered or being replaced by child themes:

echo get_theme_file_uri( '/img/bridge_ico.png' );