如何从jpg和png图像中删除元数据

Question

This should be a pretty trivial programming task in C#, however after I have searched a while I simply cannot find anything relevant on how to remove metadata. I want to remove jpg and png image metadata such as: folder path, shared with, owner and computer. My application is an MVC 4 application. In my website users can upload an image I get this image at this ActionResult method

 if (image != null)
            {
                photo.ImageFileName = image.FileName;
                photo.ImageMimeType = image.ContentType;
                photo.PhotoFile = new byte[image.ContentLength];
                image.InputStream.Read(photo.PhotoFile, 0, image.ContentLength);
            }

Photo is a property in the model, goes like this.

public byte[] PhotoFile { get; set; }

I imagine the way to remove above mentioned metadata or just all metadata, would be to use some coding like this

if (image != null)
            {
                image = image.RemoveAllMetaData; !!!

I dont mind using some 3rd party dll as long as it is compatible with NET 4.

Thanks.

Answer 1

'Metadata' here is a bit ambiguous--Do you mean the data which is required for a viewer to properly determine the image format so it can be displayed, saving only the raw image data? Or, more likely, do you mean the extra information, such as author, camera type, GPS location, etc, that is often added via the EXIF tags?

If you mean something like the EXIF data, there's a lot of programming material already on the web about how to add/modify/remove EXIF tags, and even some apps which already strips such tags: http://www.steelbytes.com/?mid=30 for example.

If you mean you just want the raw image data, you'll probably have to read and process the image first, since both JPEG and PNG do not contain simply the raw image data; It's encoded with various methods--which is why they contain metadata to tell you how to decode it in the first place. You'll have to learn/explore the JPEG and PNG data formats to extract the original raw image data (or a reasonable facsimile in the case of a "lossy" encoding).

All the above is well-documented on various websites which can be found on Google, and many include image manipulation libraries which can handle these chores for you. I suspect you just didn't know to search for something like "JPEG PNG EXIF METADATA".

BTW, EXIF applies to JPEG's, where EXIF is, loosely (and not fully technically correct) an addition of data (extension) to the end of the JPEG file, which can usually simply be truncated to remove. A quick Google search for me turned up something like libexif.sourceforge.net and other similar results.

I'm not entirely certain about the PNG format, but I believe the PNG format (which does call such items "metadata" as well) was written to include such data as part of the file format rather than an "extension" tagged on after the fact like EXIF is. PNG, however, is open source, and you can obtain libraries and code for manipulating them from the PNG website (www.libpng.org).

Answer 2

Do what all the social media websites do. Create a new image file, stream in the image byte data and use the file you created than the original one that was uploaded. Of course, now you will need to find out the original image's color depth and so on so that the image you create is not of a lower quality -- unless you need to do a disk or image resize as well.

Answer 3

There's an app for that but it's written in Perl. It doesn't recompress the image and it's here http://www.sno.phy.queensu.ca/~phil/exiftool

Found it in this thread How to remove EXIF data without recompressing the JPEG?