判断文件是否是图片

1. private bool IsPicture(string filePath)//filePath是文件的完整路径  
2.         { 
3.             try 
4.             { 
5.                 FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read); 
6.                 BinaryReader reader = new BinaryReader(fs); 
7.                 string fileClass; 
8.                 byte buffer; 
9.                 byte[] b=new byte[2]; 
10.                 buffer = reader.ReadByte(); 
11.                 b[0] = buffer; 
12.                 fileClass = buffer.ToString(); 
13.                 buffer = reader.ReadByte(); 
14.                 b[1]=buffer; 
15.                 fileClass += buffer.ToString(); 
16.  
17.  
18.                 reader.Close(); 
19.                 fs.Close(); 
20.                 if (fileClass == "255216 ")//255216是jpg;7173是gif;6677是BMP,13780是PNG;7790是exe,8297是rar  
21.                 { 
22.                     return true; 
23.                 } 
24.                 else 
25.                 { 
26.                     return false; 
27.                 } 
28.             } 
29.             catch 
30.             { 
31.                 return false; 
32.             } 
33.         }