Images are not embedded into HTML files, they are referenced. HTML files are just text files, they tell the browser where to find the content.
That is the HTML document tells the browser where to find the image files, in your case the folder in the same directory.
MS Word documents embed the image into the document, so .doc file actually contains the image data as well as the text.
To solve your problem you must send the HTML document and the directory with all of the images.