There's a lot of variations to this. I don't know how much I believe, but the outline of a child in Giygas's second form (where you're supposed to start praying) is clearly intentional. At first glance, it looks like it's just a souped-up repetition of the sprite from Giygas's first form, but if you look closer you can see alterations have been made which define the child's mouth and nose. Here are the screen shots I took from my own play through, which have been in no way altered. Look at the black space and ignore the red.
The first image shows the child's head and upper body. The second shows a more complete picture, including the child's midsection and a pair of upstretched legs. The third image, which was not made by me, shows the full image with enhancements to make the shape more visible, as well as the room leading up to Giygas, which some have claimed vaguely resembles the female reproductive system.