PSI - Issue 84

Angelo Masi et al. / Procedia Structural Integrity 84 (2026) 321–328

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inspection forms and the need for clearer typological identification to improve defect interpretation and long-term condition tracking.

4. Challenges in inspection procedures Beyond the limitations of the official inspection form, a major challenge emerging from the analysis concerns the pronounced heterogeneity of photographic devices used during inspection activities. Fig. 6 shows the device type distribution related to 1800 bearing inspection pictures taken by different inspectors belonging to the same road authority. Data were retrieved through exif metadata attached to each photograph. As can be noted, images were acquired using a wide range of instruments, including smartphones, tablets, conventional digital cameras, and drones equipped with sensors of different performance levels. In more than half of the cases, information regarding the acquisition device are not available (N.D.) The distribution of devices shows a significant reliance on mobile devices, such as smartphones and tablets (18.6%), alongside a non-negligible use of low- to medium-range cameras (8.0%) and drones (21.9%). While the adoption of drones allows access to otherwise unreachable areas, the overall heterogeneity of acquisition systems inevitably leads to inconsistencies in image quality, geometry, and radiometric characteristics. This lack of standardization is even more critical since the images were provided by just one road authority. Expected heterogeneity could be even higher considering more road management bodies.

Fig. 6. Distribution of image acquisition devices over 1800 inspection images by one road authority.

The variability in photographic equipment is directly reflected in the wide dispersion of image resolution observed in the dataset. The analysis reveals a broad range of megapixel values (from about 2.0 to over 20 MPx), with a relatively low average resolution (about 8 MPx) and a high coefficient of variation (0.52), indicating a lack of uniformity in the visual information available for inspection purposes. This dispersion affects the detectability and interpretability of small-scale defects, particularly those related to surface degradation, material extrusion, or early stage deterioration. Several images lack sharpness, denoting an insufficient accuracy in photographic documentation. Low-resolution images, which are frequently associated with mobile devices and low-end cameras, limit the ability to identify subtle damage features and may compromise the reliability of defect classification. Conversely, higher resolution images acquired with advanced cameras or drones are less common and unevenly distributed, further contributing to inconsistencies in inspection outcomes. Beyond resolution, the use of smartphones and tablets introduces additional limitations related to illumination conditions. These devices typically lack adequate lighting systems, such as external flashes or controlled illumination