Hi,
I am not sure on what is happening, images should be reliable, if they are supported. I see that you are using TBitmap.Canvas.BeginScene so I think this is firemonkey? Is it a Windows app or some other platform? Note that in other platforms other than Windows, EMF and WMF won't work, since the graphics engines outside windows don't understand those images.
Can you send me to adrian@tmssoftware.com some examples of Excel files that don't work so I can get a better idea? If possible, also attach the original image you used to embed.