hi there
afterm uch customization i was able to find the answer, if not for you then for whoever finds this, i know it can be frsutrating
to change login button
change this
echo '<input type="submit" name="Submit" class="button'.$class_sfx.'" value="'._BUTTON_LOGIN.'" />';
if ($horizontal) echo "test"; else echo "</td></tr>\n<tr><td>";
to this
echo '<input type="image" src="
yoursitehere.com/picname.png" name="Submit" class="button'.$class_sfx.'" value="'._BUTTON_LOGIN.'" />';
if ($horizontal) echo "test"; else echo "</td></tr>\n<tr><td>";
can be found on line 537 or so, hope this helps you and have fun!