Well, I would ask your landlord about it.
This has happened to me and it scared me, but what was explained to me was that it was actually the bank and the insurance company taking pictures to document the value of the home and make sure they had the correct amount of coverage on it.
Being in the insurance industry myself, it made perfect sense to me since many property owners seek quotes or to have their insurance carriers changed and the prospective carriers need documentation of the value.
For instance, a person could try to take out a million dollar policy on a property that isn't worth $45,000. The insurance company is not going to accept that "risk".
By the same token, if someone is trying to refinance their home, the bank will want to document the face value of the property.
I had a trippy ex husband who followed me around and drove past my place of employment, so when I saw some guy across the street taking pictures, my blood pressure went up. I was usually at work and I thought it strange someone would be taking pictures of my house (or me) when I was home.
My landlord told me that it was all legit and that next time they would let me know someone was coming out.
Ask your landlord and go from there.