I am currently working on an SSRS template that extracts most of the format information from a database. Some of this format information sets the background image of the cells.
I am currently filling out the image by setting Source to External and pulling its value from the database. This works fine, but it does mean that you extract an image from a network source each time, and with a small effect of efficiency, I would like to try to remove this attraction, if possible, by inserting standard images.
Again it works great, I can pull out either an external image or an embedded image and display on the screen. The problem arises when I want it too. I found that I can not set the image source from the field, there is no possibility in the GUI.

I tried to enter the code and enter the data there, but I got a validation error:
The element http://scemas.microsoft.com/sqlserver/reporting/2008/01/reportdefinition:Source is invalid - the value is =First(Fields!bodyBackgroundImageSource.Value, "dsTemplate")invalid according to its data type String- enumeration restriction is not fulfilled. "


Has anyone else come across this and found a solution or was aware of a workaround? I can continue to use only external images, but prefer to avoid as many external calls as possible.