I wanted to make a new thread but figured it's not THAT important. But I have a new theory. I think Spidey's costume fades to black throughout the movie and if we see venom he won't have the webbing because by that time it will have faded to full black.
Notice how people were discussing the released photos of Spider-man. In some shots the blue part of the costume is clearly blue. In others, even in light, it is darker. And in even others still it gets to a point where it's black?
Seeing that gradual change and then taking into account the photo of the black and white spider-man costume. I think the symbiote won't take control of him right away, but will slowly absorb his powers. Slowly tainting him, and then when it's(the original costume) fully black it'll be that picture we saw. Then when the webbing fades, it'll begin to look more like classic venom.
Just my hypothesis.