Vassil Lunchev, CEO of Homeheed (https://www.homeheed.com/) presented at our July Meetup how to detect fake listings using #ComputerVision and #MachineLearning. Imagine that you have 600,000 real estate listings with a total of 5,000,000 photos. What you know is that many of these listings are fake and some of the challenges Vassil shared in his presentation how you can detect the fake ones including the approach that works, and those which do not. Apart from that, he presented what kind of additional data is necessary to detect the fake ones.

1. Computer Vision
in Real Estate
PRESENTED BY VASSIL LUNCHEV
WWW.HOMEHEED.COM

2. There is a problem in
Sofia’s Real Estate
 Demo 1

3. Setup
There are many duplicates
We have 600,000 listings
Many listings are fake
Goals
Cluster all listings into Homes
Classify homes as available or
not-available (as of today)

4. Approaches (for clustering)
1. Location (GPS coordinates)
• Works great for Booking, Airbnb, Expedia
• Only 24% of the listings have GPS coordinates
• Even if a listing has location, it is ”wrong”
2. Texts, numbers and categories
• Price, m2, district, text description, …
• (demo 2)
3. Images

5. The image based approach
1. Find equal images
• Dataset of 5,000,000 images
• Keypoint matching
2. Given 2 listings, classify equal or non-equal
• 1 listing has about 10 images
• Machine learning classification
3. Is this home available today?
• 2 main signals – history and reputation
• Ground truth dataset

6. Finding
equal images
 Demo 3

7. Keypoint matching
1. Detect keypoings
• 500 keypoints per image
2. Describe keypoints
• 256 bits (32 bytes) per keypoint
3. Match keypoints
• Hamming distance < THRESHOLD
• Locality Sensitive Hashing (LSH)
4. Match images
• RANSAC and homography

8. Keypoint detection

9. Keypoint detection

10. Keypoint description
256 bits
1 0 0 0 1 1 0 1 0 1 0 0 1 1 0 0

11. Keypoint matching
Keypoint 1 (256 bits) 1 0 0 0 1 1 0 1 0 1 0 0 1 1 0 0
Keypoint 2 (256 bits) 1 0 1 0 1 1 0 1 0 0 0 0 1 1 0 0
XOR
=
Result 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0
Hamming distance: 2 <= 3 (constant THRESHOLD) => These keypoints are equal

12. Keypoint matching
I think this keypoint is equal to that keypoint

13. Image matching
I think the left image is equal to this part of the right image

14. The image based approach
1. Find equal images
• Dataset of 5,000,000 images
• Keypoint matching
2. Given 2 listings, classify equal or non-equal
• 1 listing has about 10 images
• Machine learning classification
3. Is this home available today?
• 2 main signals – history and reputation
• Ground truth dataset
✓ Presentation
up to now

15. Given 2 listings, classify equal or
non-equal
 Random forest
 Sources:
 Image matches (each listing has about 10 images)
 Uniqueness of the images
 Numeric data (price, square meters, floor, year, …)
 Category parameters (neighborhood, apartment type, build type, …)
 Text data (bag of words from description)
 Features are differences not absolute values

16. Is this home available today?
 3 shades of fakeness
• Available means “you can get in that home today”
• Fake means “this home has never existed”
• Outdated means “This home is already rented/sold”
 Classification per day
• Is this available (without a date) can be
both True and False (Schrödinger’s listing)
• A user looking at a snapshot of a listing (just today) misses
most of the information
Disclaimers:

17. Is this home available today?
2 main signals
• Home history (new and removed listings)
• Lister reputation (how much I trust this guy)
Ground truth dataset
• Manual labeling of auto generated candidates
• The book a showing feature of Homeheed

18. QUESTIONS…