How to force Media manager to overwrite files of same name?

Question

I have a widget that works with my theme that expects images named in a certain way, slide1.png, slide2.png, etc...

However, when the user uploads their own images, named slide1.png, slide2.png, etc to the media library, rather than updating the images with the new ones, WordPress changes the names of the replacement images to slide11.png, slide22.png, etc

Can I set a filter in theme options that tells WP to overwrite existing images without changing the filenames?

Answer 1

Here is something i cooked up which was taken mainly from the plugin Overwrite Uploads but without the extra stuff

add_filter('wp_handle_upload_overrides','noneUniqueFilename');
function noneUniqueFilename($overrides){
    $overrides['test_form'] = false;
    $overrides['unique_filename_callback'] = 'nonUniqueFilenameCallback';
    return $overrides;
}

function nonUniqueFilenameCallback($directory, $name, $extension){
    $filename = $name . strtolower($extension);
    //remove old attachment
    removeOldAttach($filename);

    return $filename;
}

function removeOldAttach($filename){
    $arguments = array(
        'numberposts'   => -1,
        'meta_key'      => '_wp_attached_file',
        'meta_value'    => $filename,
        'post_type'     => 'attachment'
    );
    $Attachments_to_remove = get_posts($arguments);

    foreach($Attachments_to_remove as $a)
        wp_delete_attachment($a->ID, true);
}

Answer 2

I managed to make this work using a bit of @Bainternet's Answer without hacking the core.

This other Q&A was helpful as well: query_posts: how to show all 'meta_value' containing a specific word?

The function wp_unique_filename has the filter sanitize_file_name just at the beginning, so we can hook there and do the checking and removal of the duplicate attachment.

I did basic localhost testings, please test it thoroughly before applying to a live site.

add_filter( 'sanitize_file_name', 'filename_filter_wpse_28439', 10, 1 );

function filename_filter_wpse_28439( $name ) 
{
    $args = array(
        'numberposts'   => -1,
        'post_type'     => 'attachment',
        'meta_query' => array(
                array( 
                    'key' => '_wp_attached_file',
                    'value' => $name,
                    'compare' => 'LIKE'
                )
            )
    );
    $attachments_to_remove = get_posts( $args );

    foreach( $attachments_to_remove as $attach )
        wp_delete_attachment( $attach->ID, true );

    return $name;
}