Any ...html file is a webpage (or page construct) and a JPG is an image. It is not quite as simple, as you might imagine, to convert a webpage into an image, unless you want to do it manually.
To do so manually, it is just a screen capture. But if any part of that webpage is not on the screen at the time of the capture, then it will not automatically be included into the JPG (or any image).
It is possible to "stitch" multiple images together to merge multiple images together to create one image, but that, in most cases, is not an automatic function.
Now, if you want to learn how to do a screen capture, we can tell you that.
But, unless I am wrong (not impossible), the actions you are hoping for can not be done with a simple program.
I work with files that contain photos & text. Many are listed as MHTML files. I need to convert them to JPG in order to be able to place them on certain sites. Can anyone out there help me. I have had no luck at finding a online converter for this type of file.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic