ขอความช่วยเหลือหน่อยนะค่ะ กดปุ่มล้างข้อมูลเเล้วรูปไม่หายอ่ะค่ะ

<script language="JavaScript">
	function showPreview(ele)
	{
			$('#imgAvatar').attr('src', ele.value); // for IE
			if (ele.files && ele.files[0]) {

				var reader = new FileReader();
				
				reader.onload = function (e) {
					$('#imgAvatar').attr('src', e.target.result);
				}

				reader.readAsDataURL(ele.files[0]);
			}
		}
		</script>
<form action="material.php" method="post" id="form" enctype="multipart/form-data">


                        						<div class="col-sm-2">รหัสวัสดุ</div>
                        						<div class="col-sm-3"><input class="form-control" style="width:200px;" id="mat_id" name="mat_id" type="text" readonly="readonly" value="<?=$mat_id?>"></div>
                        						<div class="col-sm-2">ชื่อวัสดุ<font color="red">&nbsp; *</font></div>
                        						<div class="col-sm-5"><input class="form-control" id="mat_name" name="mat_name" style="width:200px;"></div>

                        						<div class="col-sm-2" >สี<font color="red">&nbsp; *</font></div>
                        						<div class="col-sm-3" ><select name="color_id" class="form-control" style="width:200px;">
                        							<?php
                        							$result = mysql_query("SELECT * FROM color ORDER BY color_name") or die(mysql_error());
                        							while ($row = mysql_fetch_array($result)) 
                        							{
                        								?>
                        								<option value="<?php echo $row["color_id"]?>"><?php echo $row["color_name"]?></option>
                        								<?php
                        							}
                        							?>
                        						</select> 
                        					</div>

                        					<div class="col-sm-2" >ยี่ห้อ<font color="red">&nbsp; *</font></div>
                        					<div class="col-sm-5" ><select name="brand_id" class="form-control" style="width:200px;">
                        						<?php
                        						$result = mysql_query("SELECT * FROM brand ORDER BY brand_name") or die(mysql_error());
                        						while ($row = mysql_fetch_array($result)) 
                        						{
                        							?>
                        							<option value="<?php echo $row["brand_id"]?>"><?php echo $row["brand_name"]?></option>
                        							<?php
                        						}
                        						?>
                        					</select>
                        				</div>


                        				<div class="col-sm-2" >ประเภทวัสดุ<font color="red">&nbsp; *</font></div>
                        				<div class="col-sm-3" ><select name="typemat_id" class="form-control" style="width:200px;">
                        					<?php
                        					$result = mysql_query("SELECT * FROM type_material ") or die(mysql_error());
                        					while ($row = mysql_fetch_array($result)) 
                        					{
                        						?>
                        						<option value="<?php echo $row["typemat_id"]?>"><?php echo $row["typemat_name"]?></option>
                        						<?php
                        					}
                        					?>
                        				</select> 
                        			</div>
                        			<div class="col-sm-2" >จุดสั่งซื้อ<font color="red">&nbsp; *</font></div>
                        			<div class="col-sm-5" ><input class="form-control" id="mat_point_order" name="mat_point_order" style="width:200px;" ></div>



                        			<div class="col-sm-2" >จำนวน<font color="red">&nbsp; *</font></div>
                        			<div class="col-sm-3" ><input class="form-control" id="mat_amount" name="mat_amount" style="width:200px;"></div>

                        			<div class="col-sm-2" >หน่วยนับ<font color="red">&nbsp; *</font></div>
                        			<div class="col-sm-5" ><select name="unit_id" class="form-control" style="width:200px;">
                        				<?php
                        				$result = mysql_query("SELECT * FROM unit WHERE typeun_name = 'สินค้า'") or die(mysql_error());
                        				while ($row = mysql_fetch_array($result)) 
                        				{
                        					?>
                        					<option value="<?php echo $row["unit_id"]?>"><?php echo $row["unit_name"]?></option>
                        					<?php
                        				}
                        				?>
                        			</select> 
                        		</div>

                        		<div class="col-sm-2">ราคาต้นทุน (บาท)<font color="red">&nbsp; *</font></div>
                        		<div class="col-sm-10"><input class="form-control" id="costprice" name="costprice" style="width:200px;"></div>

                        		<div class="col-sm-2" >รูปภาพ<font color="red">&nbsp; *</font></div>
                        		<div class="col-sm-10" display:inline>
                        			<input name="mat_pic" id="file_upload"  type="file" size="35"/ OnChange="showPreview(this)">
                        			<!--<div id="upload" class="btn btn-info">   style="display:none" 
                        			เลือกไฟล์
                        		</div>  -->
                        	</div>
                        	<div class="col-sm-2" ></div>
                        	<div class="col-sm-10"> <div id="thumbnail"></div>   </div>

                        	<div class="col-sm-6"><button type="submit" class="btn btn-success " value="submit" name="submit" style= "width: 80px; float: right;">เพิ่มข้อมูล</button></div>
                        	<div class="col-sm-6"><button type="reset" class="btn btn-danger " style="width: 80px; float: left;">ล้างข้อมูล</button></div>

                        </form>