I have a similar problem so maybe we can help each other. I created signatures (mine and ones for co-workers) in Word on my Mac and have had mild success in copy-pasting into Outlook for Mac. I created it as a table on Word to help keep the format I want. It typically will pull over images and formatted text (some with hyperlinks) successfully but will adjust text and image sizes, typically making them larger than expected. With trial & error adjustments in Word, I can get it to copy-paste into Outlook with the perfect layout. However, if I send that file to another computer (Mac or PC), it isn't the same for them.
So I have to make the adjustments in Word on each computer. So I'm not sure how to make it consistent in its results. Now, what I think may help you, when I tried to send it to a PC (coming from a Mac), the image created the X for me.
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I had to re-add the image on the PC (if I remember correctly, I just right-clicked replace) and then it worked.