Making a dynamic image appear blank

I am putting some dynamic images in some reports.  Some records do not include an image file path.  So instead of the default image I used to set it up, the client would like nothing to appear.

I have tried the code below in the Graphic Location formula to use a path that does not exist and I tried "" instead of the temp path, but it still shows the default I set it up with.

If {CustomerInvoices.CompanyLogoPath} = "" then

    "c:\temp\temp.bmp"

else

    {CustomerInvoices.CompanyLogoPath}

The only solution I have come up with is to use an actual image of a blank, hopefully transparent canvas as a png file as the default so it will not show at all and not show as a white background on colour paper.

Does anyone else have any ideas?

TIA, rasinc