直接写死路径试试

web/admin/md_check.php

@@ -24,7 +24,7 @@ function MarkdownEntities($markdown) {
         return str_replace(['<', '>'], ['\\lt', '\\gt'], $matches[0]);
     }, $markdown);
     // 对图片内容存储到本机并替换
-    $saveDir = __DIR__ . "/../upload/markdown";
+    $saveDir = "/home/judge/src/web/upload/markdown";
     $markdown = preg_replace_callback('/!\[.*?\]\((.*?)\)/', function ($matches) use ($saveDir) {
         $imageUrl = $matches[1];
         $savedPath = downloadImage($imageUrl, $saveDir);