If file exists with page slug name show image else nothing

EDITED ANSWER – First get the full file path to your image and store it to a variable $filename. Use file_exists to check if image exists, and output the image and with it the title of your image. If the condition fails, there is no output. https://codex.wordpress.org/Function_Reference/wp_upload_dir

 <?php

    global $post;
    $slug = get_post( $post )->post_name;  //get current page slug
    $image_name = $post->post_title;  //get page name
    $upload_dir = wp_upload_dir(); 
    //file_exists needs to check full file path of your hard drive instead of url:
    $filename = $_SERVER['DOCUMENT_ROOT']."/wp-content/uploads/" . $slug. '.jpg'; 
    //echo $filename; 

    if (file_exists($filename)) {  //output only when matched
      echo '<img src="'. $upload_dir['baseurl']."https://wordpress.stackexchange.com/" . $slug.'.jpg'.'"  title="'.$image_name.'" alt="" >';  
    } else {}

    clearstatcache();  //clear cache results of file_exists
   ?>