(Back from the motherland!)
Re Goa:
I found out that since the portuguese had forbidden what they called idol worship, Goans used to paint Ganesha, Shankar etc on paper and worship these. Reason was that it was easier to hide these pieces of paper (compared to "idols") if the inquisition came into your house. Paper painting worship continues to this day, but is done on a small scale in parallel with vigraha pooja. Shiva, Parvati, and Ganesh paintings are worshipped next to the murti in Ganeshchaturthi days.
Re Goa:
I found out that since the portuguese had forbidden what they called idol worship, Goans used to paint Ganesha, Shankar etc on paper and worship these. Reason was that it was easier to hide these pieces of paper (compared to "idols") if the inquisition came into your house. Paper painting worship continues to this day, but is done on a small scale in parallel with vigraha pooja. Shiva, Parvati, and Ganesh paintings are worshipped next to the murti in Ganeshchaturthi days.