检测一个图片是否是真实图片

主要是判断,图片上传后的操作，判断是否真的是图片

代码:

try

{

HttpPostedFile postfile = Request.Files["file"];

string savepath = Server.MapPath("Image/" + postfile.FileName);

postfile.SaveAs(savepath);

FileStream fs = new FileStream(savepath, FileMode.Open, FileAccess.Read);

BinaryReader reader = new BinaryReader(fs);

string fileClass;

byte buffer;

byte[] b = new byte[2];

buffer = reader.ReadByte();

b[0] = buffer;

fileClass = buffer.ToString();

buffer = reader.ReadByte();

b[1] = buffer;

fileClass += buffer.ToString();

reader.Close();

fs.Close();

if (fileClass == "255216" || fileClass == "7173" || fileClass == "6677" || fileClass == "13780")//255216是jpg;7173是gif;6677是BMP,13780是PNG;7790是exe,8297是rar

{

Response.Write("图片可用");

}

else

{

Response.Write("图片非法");

File.Delete(savepath);

return;

}

}

catch (Exception)

{

Response.Write("图片非法！");

return;

throw;

}