You need to use a code like

$upload_Name1 = $_FILES[$file_key]['name'];
$upload_Name = $prefix.str_replace(" ", "_", $upload_Name1);
$upload_Size = ($_FILES[$file_key]['size']);
$upload_Temp = ($_FILES[$file_key]['tmp_name']);
$upload_Type = ($_FILES[$file_key]['type']);
if($upload_Type != "image/gif" AND $upload_Type != "image/pjpeg" AND $upload_Type != "image/jpeg" AND $upload_Type != "image/png" AND $upload_Type != "image/tiff" AND $upload_Type != "image/bmp"){
$error1 = "$file_key file type is '$upload_Type' which is not allowed! \n";
// Add here a "include" command to include an error page
}

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