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I'm working on a project where I find JPG files using a folder dialog and list the images in a list.

Now, I've extended the program so the user can just drag and drop files in the list. But I want the images to be JPG.

I check for image size, width and height, and other as shown below....

C#
public bool IsValid(string FileName)
       {
           Photo JPGFile = new Photo(FileName);

           //Check if the file exists.
           if (!System.IO.File.Exists(JPGFile.FullPath)) { return false; }

           //Check if the File is a JPG File.
           if (System.IO.Path.GetExtension(FileName).ToLower() != ".jpg")
           {
               //<-------------------------------Need a better validation------------>
               return false;
           }

           //Check if the FilePath Matches any other file in the List.
           foreach (Photo Picture in Photos)
           {
               if (FileName == Picture.FullPath)
               {
                   return false;
               }
               else
               {
                   continue;
               }
           }

           //Check if the File Size is greater than 450kb.

           if (JPGFile.GetRawSize() > 450)
           {
               return false;
           }

           //Check if the Height or width of the image is greater than that of the screen size.

           if (JPGFile.ImageWidth > SystemParameters.VirtualScreenWidth || JPGFile.ImageHeight > SystemParameters.VirtualScreenHeight)
           {
               return false;
           }

           return true;
       }


When I was testing, I just renamed a desktop.ini file to Desktop.jpg and it passed validation. Can anyone help please on how I can really check if the image is a VALID jpg file.

Thanks.
Posted

The easiest way is to open it as an image and check it's a JPG type when it's open. However, if it isn't then you will get an exception which may not always be catchable.

A safer way is to open the file as a binary stream and check the start and end: JPG files start with the two bytes 0xFF and 0xD8, and end with the two bytes 0xFF and 0xD9. There are also some specific ASCII strings in JPG files: http://en.wikipedia.org/wiki/Magic_number_%28programming%29#Magic_numbers_in_files[^]
If these are present, it probably is a JPG. But the only true way to be absolutely sure is to load it as an image!
 
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try this:

public  bool IsJpegImage(string filename)
{
	try
	{
		System.Drawing.Image img = System.Drawing.Image.FromFile(filename);

					   
		return img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Jpeg);
	}
	catch (OutOfMemoryException)
	{
		return false;
	}
} 
 
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v2
Comments
Prasad_Kulkarni 16-Jul-12 5:13am    
Exact one +5!
Manas Bhardwaj 16-Jul-12 5:54am    
thx!
Akinmade Bond 15-Oct-12 12:11pm    
+5. Do you know any WPF approach to do the exact same thing?

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