Downstream pebble variability in river systems is assessed through various methods, with recent emphasis on efficient, time-saving semi-automatic processes involving photography and digital analysis. The Inaouène Valley, however, lacked a comprehensive survey of its main channel using either manual or image-based methods. This study bridges this gap by combining both approaches to analyze the downstream evolution of surface pebbles' morphometric parameters along approximately 60 km of the Inaouène's middle reach. Our research focuses on two key aspects: grain size and particle shape. Results reveal a general downstream trend of size fining, increasing circularity and decreasing elongation, primarily attributed to abrasion and travel distance. Notably, this pattern is interrupted by localized variations associated with tributary inputs and sediment recycling processes. This study significantly contributes to the understanding of fluvial sediment dynamics in the Inaouène Valley. Its findings have broad implications, supporting ecological assessment and restoration efforts, while also informing decision-making in river engineering and management. By providing a comprehensive analysis of pebble characteristics and their downstream evolution, this research establishes a foundation for future geomorphological studies and practical applications in river system management.