If you want to check if a JPEG image is progressive you should check if the Interlace property of the MagickImage is set to Jpeg. And if you want to change it to baseline you should set the Interlace property to NoInterlace. Be aware that JPEG is lossy so you should only want to write the image if the Interlace property is Jpeg. In the next version of Magick.NET (7.0.0.022) you will be able to use the MagickImageInfo class to quickly check the Interlace value of an image. This will help you if you need to process a lot of images.
p.s. Thanks for posting the message here also :)
p.s. Thanks for posting the message here also :)