I'm pretty sure, that only the people with 0 km will have a chance to win.
I do a lot of competitions every month.
In fact I'm quite a competition fanatic.
Some time ago I participated in a similar competition, where they showed you pictures of streets in France, which are located in tourist areas.
You had a map and you had to mark where the street could be located.
You got points based on how close you got to the actual street.
The main prize was a car and you had to reach a certain number of points to be able to have a chance to win the car.
Everyone who had less than a certain number of points only had a chance to win a small prize.
Everything was explained in the terms and conditions of the competition.
Since the goal of this competition is to find the place where the album cover was taken and nothing else regarding points/km is mentioned the only thing that counts is the distance.
So 0 km is better than 3 km or 50 km.
The reason why they mention that you participate with 70 km is that they don't know how many people will reach 0 km.
If there a 50 people who reach 0 km and 100 who reach 3 km they will draw the prizes among the ones with the better results.
But if there's 1 person who reached 0 km and 50 people with 3 km you would a chance to win with 3 km.
This is a quite common method to narrow down the number of participants for a competition, because it's unlikely that everyone will reach 0 km. Of course everyone has the same chance in the beginning, but the prizes will be drawn among the best participants.