New Post: Detect compression method with MagickImageInfo

You can use the Ping method of MagickImage to read only the basic information of an image. This is kind of what the MagickImageInfo class does. I will add a Compression property to the MagickImageInfo class in the next release.

But I don't think that pinging a MagickImage and then reading the compression property will help you. The compression property is never set to RLE in the jpeg decoder of Magick.NET.

It might be possible that your GDI+ issue gone when you lossless compress the image (https://magick.codeplex.com/wikipage?title=Lossless%20compression&referringTitle=Documentation). Maybe you should give that a try? This will really reduce the size of your file also!