<?php
class Mastodon
{
    const host = "mstdn.jp";
    const endpoint1  = "/api/v1/statuses";
    const endpoint2  = "/api/v1/media";

    public function toot($text){
        $data = array('file' => new CURLFile("/var/www/html/t_m/image.png", 'image/png', "image.png"));
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, "https://" . self::host . self::endpoint2);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
        curl_setopt($ch, CURLOPT_HTTPHEADER, ['User-Agent: ' . $_SERVER['HTTP_USER_AGENT'], 'Content-Type: multipart/form-data', 'Authorization: Bearer ' . MSTDN_ACCESSTOKEN]);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);
        $response =   json_decode(@curl_exec($ch));
        curl_close($ch);
        if (isset($response->id)) {
            $postdata = [
                "visibility" => "public",
                "media_ids" => [$response->id],
                "status" => strip_tags($text),
            ];
            $data = json_encode($postdata);
            $ch = curl_init();
            curl_setopt($ch, CURLOPT_URL, "https://" . self::host . self::endpoint1);
            curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
            curl_setopt($ch, CURLOPT_HTTPHEADER, ['User-Agent: ' . $_SERVER['HTTP_USER_AGENT'], 'Content-Type: application/json', 'Authorization: Bearer ' . MSTDN_ACCESSTOKEN]);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
            curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
            curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
            $response =  @curl_exec($ch);
            curl_close($ch);
        }
    }
}

php Mastodon.php 'テスト投稿です'

<?php
require "config.php";
class Mastodon{
    const method = "POST";
    const host = "mstdn.jp";
    const endpoint  = "/api/v1/statuses";
    public static function toot($postdata = null)
    {
        if(!is_null($postdata)){
            $data = http_build_query($postdata);
            exec('curl -X POST -d "'.$data.'" --header "Authorization: Bearer '.ACCESSTOKEN.'" -sS https://'.self::host . self::endpoint.'; echo $?',$output);
            var_dump($output);
        }
    }
}
//    「未収載」    -> 'unlisted'
//    「公開」      -> 'public'
//    「非公開」    -> 'private'
//    「ダイレクト」 -> 'direct'
if($argv[1]){
    $postdata = [
        "visibility"=>"public",
        "status"=>strip_tags($argv[1]),
    ];
    Mastodon::toot($postdata);
}

<?php
define('ACCESSTOKEN','xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx');