I see a number of red flags here.
First of all, you're a recent graduate, which means, without much experience in software development.
Second, you graduated in mechanical engineering, not software.
And they give you as your first task, to recognize objects in a video stream?
That's like asking someone who went through a 6-month training in ...
My advice: bail out now before its too late. Many people here will say it's a great opportunity to learn something new and expand your skill set. But you run an even greater risk (and a realistic one at that) of the startup sinking, and everyone laid off and the bosses bail out with large cash bonuses. You'd be stuck with some vague thing you do not ...