Source

File: wp-includes/media.php

function get_image_tag( $id, $alt, $title, $align, $size = 'medium' ) {

	list( $img_src, $width, $height ) = image_downsize( $id, $size );
	$hwstring                         = image_hwstring( $width, $height );

	$title = $title ? 'title="' . esc_attr( $title ) . '" ' : '';

	$class = 'align' . esc_attr( $align ) . ' size-' . esc_attr( $size ) . ' wp-image-' . $id;

	/**
	 * Filters the value of the attachment's image tag class attribute.
	 *
	 * @since 2.6.0
	 *
	 * @param string       $class CSS class name or space-separated list of classes.
	 * @param int          $id    Attachment ID.
	 * @param string       $align Part of the class name for aligning the image.
	 * @param string|array $size  Size of image. Image size or array of width and height values (in that order).
	 *                            Default 'medium'.
	 */
	$class = apply_filters( 'get_image_tag_class', $class, $id, $align, $size );

	$html = '<img src="' . esc_attr( $img_src ) . '" alt="' . esc_attr( $alt ) . '" ' . $title . $hwstring . 'class="' . $class . '" />';

	/**
	 * Filters the HTML content for the image tag.
	 *
	 * @since 2.6.0
	 *
	 * @param string       $html  HTML content for the image.
	 * @param int          $id    Attachment ID.
	 * @param string       $alt   Image description for the alt attribute.
	 * @param string       $title Image description for the title attribute.
	 * @param string       $align Part of the class name for aligning the image.
	 * @param string|array $size  Size of image. Image size or array of width and height values (in that order).
	 *                            Default 'medium'.
	 */
	return apply_filters( 'get_image_tag', $html, $id, $alt, $title, $align, $size );
}