It is difficult to use uncertified aerial photographs for photogrammetry because?

1. **Accuracy and Quality Issues**: Uncertified photographs may not meet the required standards of accuracy, resolution, and quality necessary for precise photogrammetric measurements. This can result in unreliable data and inaccurate 3D models or maps.

2. **Lack of Calibration Information**: Certified aerial photographs come with calibration information such as camera parameters (focal length, sensor size), flight parameters (altitude, speed), and ground control points. Without this information, it is difficult to accurately reconstruct the geometry of the terrain or objects from the photographs.

3. **Georeferencing Challenges**: Certified aerial photographs are typically georeferenced, meaning their spatial coordinates (latitude, longitude, elevation) are known and accurate. Uncertified photos may lack this geospatial metadata, making it harder to align them with other spatial datasets or maps.

4. **Legal and Ethical Concerns**: Using uncertified aerial photographs may raise legal issues regarding ownership, copyright, and privacy. It's important to have permission to use and analyze aerial imagery, especially if it involves public or private property.

5. **Reliability in Analysis**: Photogrammetry relies on precise measurement and analysis of image features. Uncertified photographs may have inconsistent lighting conditions, distortions, or artifacts that can affect the accuracy and reliability of the photogrammetric results.

In summary, certified aerial photographs provide the necessary metadata, accuracy, and quality assurance required for reliable photogrammetric analysis. Uncertified photographs lack these assurances, making them less suitable and more challenging to use effectively in photogrammetry applications.