The answer for this one is the first image is the most recent making it a 5. The fourth image is the second most recent making it a 4. The second image is a 3. The third image is a 2. And the 5th image is a 1.
To simplify: (in left to right) Image 1: 5 (most recent)
Image 2: 3
Image 3: 2
Image 4: 4
Image 5: 1 (least recent)
Hope this helps!!!