stop my wordpress site from creating multiple sizes of images

hi all i am using wordpress 3.5 and zBench theme on my selfhosted site..

my site is basically full of images and it will only contain images as primary content..but the problem is whenever i upload images to my posts WP is automatically generating 2 more sizes…

i have already tried setting values to 0px in media settings for thumb size of small,medium and large…but still this problem persists…

i also tried putting below code to my functions.php file…

function sgr_filter_image_sizes( $sizes) {

unset( $sizes[‘thumbnail’]);
unset( $sizes[‘medium’]);
unset( $sizes[‘large’]);

return $sizes;
}
add_filter(‘intermediate_image_sizes_advanced’, ‘sgr_filter_image_sizes’);

but didn’t worked…is there any way to stop WP creating several sized images..i want only original one…