C# How can I test a file is a jpeg?

Question

Using C# how can I test a file is a jpeg? Should I check for a .jpg extension?

Thanks

Answer 1

The code here:

http://mark.michaelis.net/Blog/RetrievingMetaDataFromJPEGFilesUsingC.aspx

Shows you how to get the Meta Data. I guess that would throw an exception if your image wasn't a valid JPEG.

Answer 2

Depending on the context in which you're looking at this file, you need to remember that you can't open the file until the user tells you to open it.

(The link is to a Raymond Chen blog entry.)

Answer 3

The best way would to try and create an image from it using the Drawing.Bitmap (string) constructor and see if it fails to do so or throws an exception. The problem with some of the answers are this: firstly, the extension is purely arbitrary, it could be jpg, jpeg, jpe, bob, tim, whatever. Secondly, just using the header isn't enough to be 100% sure. It can definitely determine that a file isn't a jpeg but can't guarantee that a file is a jpeg, an arbitrary binary file could have the same byte sequence at the start.

Answer 4

You could try loading the file into an Image and then check the format

Image img = Image.FromFile(filePath);
bool isBitmap = img.RawFormat.Equals(ImageFormat.Jpeg);

Alternatively you could open the file and check the header to get the type

Answer 5

Read the header bytes. This article contains info on several common image formats, including JPEG:

Using Image File Headers To Verify Image Format

JPEG Header Information

Answer 6

You can use the Path.GetExtension Method.