how to show images without passing it to timthumb.php file for resizing

add the size to your images sizes using add_image_size() to your theme’s functions.php file. eg:

if ( function_exists( 'add_theme_support' ) ) {
    add_image_size( 'index-thumb', 220, 180 ); // 220 pixels wide by 180 pixels tall
}

then set the image as featured image from the media uploader of the posts :

then open your index.php and replace the image tag that is calling the timthumb.php file for resizing with:

if(has_post_thumbnail()) {
    the_post_thumbnail('index-thumb');
} else {
    //show default image if none is set
    echo '<img src="'.get_bloginfo("template_url").'/images/img-default.png" />';
}