Under Solidworks composer, I have a background with the "DS CATIA Composer" logo (see photo). It does not belong to the ground (nor to the shadow, nor to the mirror, nor to the grid).
I can't delete it and it appears on all extractions (images, videos...).
The mention "Trial Edition" appears on the watermark of the background, so you probably don't have to look any further for its origin and why there is no option to get rid of it.