Pictures are an important part of the booking engine. Make sure that they are in good quality and landscape orientation.
1. To upload pictures please navigate to: Settings > Booking Engine > Pictures. 
2. Here you choose the pictures you would like to upload.
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3. Once the pictures are chosen, hit import.
4. Assign pictures either to the property and per room type. Arrange them in the correct order by selecting the position (number 1 being the first picture to show).