Energy retrofit of existing buildings demands an accurate assessment of the thermal performance of the building envelope. In response, the THERMOG research project is developing a comprehensive tool to meet this requirement by delivering precise and practical insight into building envelope thermal efficiency. The paper presents the development and application of innovative algorithms for the pre- and post-processing of thermal images, specifically tailored to address challenges in analyzing 20 buildings subjected to comprehensive photogrammetric and thermographic investigations. A significant obstacle in this study was the lack of georeferencing in the thermal images, an issue that poses considerable challenges in aligning and correlating these images with their photogrammetric counterparts. To address these challenges, a novel methodology that primarily focuses on the processing of thermal images was developed, combining image processing techniques with algorithms tailored to reconstruct building facades and other areas of interest. The pre-processing phase centers on refining thermal image quality through noise reduction, image sharpening, and contrast enhancement, followed by detailed facades and reconstruction of critical building elements. Although the complete testing of this algorithm is planned for the 20 buildings, preliminary assessments have shown promising results in improving the fidelity and utility of thermal data. Also, it provides a framework for more nuanced and detailed analysis of building envelopes, which is crucial for energy efficiency diagnostics and architectural conservation.