인풋 버튼 누를때 이미지 출력

<span> <input type="button" onfocus="this.blur()" value=" 0 " onClick="enter_exp(document.fwrite.exp,' 0 ')" style="width:28px;" readonly="readonly"></span>
    <span> <input type="button" onfocus="this.blur()" value=" 1 " onClick="enter_exp(document.fwrite.exp,' 1 ')" style="width:28px;" readonly="readonly"></span>
    <span> <input type="button" onfocus="this.blur()" value=" 2 " onClick="enter_exp(document.fwrite.exp,' 2 ')" style="width:28px;" readonly="readonly"></span>
    <span> <input type="button" onfocus="this.blur()" value=" 3 " onClick="enter_exp(document.fwrite.exp,' 3 ')" style="width:28px;" readonly="readonly"></span>
    <span> <input type="button" onfocus="this.blur()" value=" 4 " onClick="enter_exp(document.fwrite.exp,' 4 ')" style="width:28px;" readonly="readonly"></span>
    <span> <input type="button" onfocus="this.blur()" value=" 5 " onClick="enter_exp(document.fwrite.exp,' 5 ')" style="width:28px;" readonly="readonly"></span>
    <span> <input type="button" onfocus="this.blur()" value=" 6 " onClick="enter_exp(document.fwrite.exp,' 6 ')" style="width:28px;" readonly="readonly"></span>
    <span> <input type="button" onfocus="this.blur()" value=" 7 " onClick="enter_exp(document.fwrite.exp,' 7 ')" style="width:28px;" readonly="readonly"></span>
    <span> <input type="button" onfocus="this.blur()" value=" 8 " onClick="enter_exp(document.fwrite.exp,' 8 ')" style="width:28px;" readonly="readonly"></span>
    <span> <input type="button" onfocus="this.blur()" value=" 9 " onClick="enter_exp(document.fwrite.exp,' 9 ')" style="width:28px;" readonly="readonly"></span>
    <span> <input type="button" onfocus="this.blur()" value=" ← " onClick="enter_exp(document.fwrite.exp,' ← ')" style="width:28px;" readonly="readonly"></span>

    <span> <input type = "button" onfocus="this.blur()" value= " 지움 " onClick="clear_exp(document.fwrite.exp)" style="width:60px"></span>

    <input id="exp" name="wr_3" value="<?php echo $wr_3 ?>"  size="30" maxlength="4" placeholder="전화번호 마지막 4자리" ></textarea>

<script LANGUAGE="JavaScript">
function enter_exp(p,str){
if(str==" ← ") p.value = p.value.substring(0, p.value.length-3);
else p.value+=str;
}
function clear_exp(p){
p.value=""
}

</script>