Redocneves

Now Code Works like:

header.php:

<?php if(is_single()): $mainheadbar_img = taxonomy_images_plugin_single_src() ?>
<?php else: $mainheadbar_img = apply_filters( 'taxonomy-images-queried-term-image-url', '', array('image_size' => 'full') );endif; ?>

functions.php

function taxonomy_images_plugin_single_src( $default, $args = array() ) {
	$filter = 'taxonomy-images-list-the-terms';
	if ( current_filter() !== $filter ) {
		taxonomy_image_plugin_please_use_filter( __FUNCTION__, $filter );
	}

	$args['having_images'] = true;

	if ( ! taxonomy_image_plugin_check_taxonomy( 'category', $filter ) ) {
		return '';
	}

	$terms = apply_filters( 'taxonomy-images-get-the-terms', '', $args );

	if ( empty( $terms ) ) {
		return '';
	}

	$output = '';
	foreach( $terms as $term ) {
		if ( ! isset( $term->image_id ) ) {
			continue;
		}
		$image_attributes = wp_get_attachment_image_src( $term->image_id, $args['image_size'] );
    $image_src = $image_attributes[0];
    break;
	}

	if ( ! empty( $image_src ) ) {
		return $image_src;
	}
	return '';
}