There were a number of B Giovannis painting during the 15th/16th centuries. There were several pictures created around this time which depict the baptism of Christ, and they may be similar to your description. It is of course impossible to say without seeing the painting in person. If you were to have an original painting from that era it would almost certainly be a valuable item, and would be the kind of thing you might well see in a museum. I suspect that your item may be some kind of print or other reproduction, but the only way to be certain is if you show the item to an auction house or art and antiques dealer in your local area. Meanwhile, you could try googling 'B Giovanni Christ Painting' in images, to see if you can see something similar to your picture.