The dbTextureBackdrop command was noted in the help files as obsolete and to be removed in a future version. So I didn't implement it.
Then it was instead put back as an official command. The next version of PureGDK will have it added back.
In the meantime, you can use the same method for plugin wrapping to create a dbTextureBackdrop command. This is the same method PureGDK will be using internally for all future versions.
The string table entries can be found in "DBProCameraDebug.dll":
TEXTURE BACKDROP%L%?BackdropTexture@@YAXH@Z%Image Number
TEXTURE BACKDROP%LL%?BackdropTexture@@YAXHH@Z%Camera Number, Image Number
So it would be:
dbTextureBackdrop%L%?BackdropTexture@@YAXH@Z%ImageID.l
dbTextureBackdrop2%LL%?BackdropTexture@@YAXHH@Z%CameraID.l, ImageID.l%ImageID.l, CameraID.l
Remember, parameters must be reordered so that optional parameters are always at the end.