You're still missing 2 double quotes though.
You could use
printf("<tr><td><font face=\"arial\" size=\"6\"><center><img src=\"files%s\" width=\"120\" height=\"120\"></center></font></td></tr>\n", $myrow0["image_name"]);
or preferably (IMO)
echo '<tr><td><font face="arial" size="6"><center><img src="files' . $myrow0["image_name"] . '" width="120" height="120"></center></font></td></tr>' . "\n";