Learn Croatian: Gledam tvoje slike, ali ne vidim tvoj automobil. - I am looking at your pictures, but I do not see your car.

They actually have slightly different meanings and form a suppletive aspectual pair (two completely different words that pair up to describe the same type of action). Gledati means to look at or to watch (the ongoing process), while vidjeti means to see (the result). Here, you are actively looking at (gledam) the pictures, but the result is that you do not spot or see (vidim) the car.

Are tvoje slike and tvoj automobil both in the accusative case here?

Yes, they are both direct objects receiving the action of the verbs. Slika is a feminine noun, and its accusative plural is slike (making it tvoje slike). Automobil is a masculine inanimate noun (not a living being), so its accusative singular looks exactly like its basic dictionary form.

Why is ne written as a separate word in ne vidim?

In Croatian, the negative word ne is almost always written separately from the verb, just like in ne vidim or ne radim. There are only four common exceptions where the negative particle and the verb combine into one word: nisam (I am not), neću (I will not), nemam (I do not have), and nemoj (do not).