Abstract: Coal seam water injection is a key technology for source control of hazards such as dust and gas. The complex pore-fracture structure within the coal mass directly determines the effectiveness of water injection, making it essential to clarify the distribution of coal’s microstructure and the underlying water seepage mechanisms. Among various techniques for characterizing coal structure, digital imaging technologies including Scanning Electron Microscopy (SEM), Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM), and X-ray Computed Tomography (CT) are widely used for analyzing coal pores and fractures due to their capabilities in visualization and quantification. This review systematically analyzes the principles, observational scales, and image processing procedures of these digital imaging technologies, discusses their effectiveness in characterizing coal pore-fracture structures and analyzing water seepage characteristics, and further prospects their future development directions in the field of coal and rock seepage. SEM, FIB-SEM, and CT collectively form a core technical system for characterizing coal pore-fracture structures from the nanometer to micrometer scale. SEM is primarily used for surface morphological analysis in two dimensions, FIB-SEM enables non-destructive three-dimensional detection of nanopores, and CT is suitable for the three-dimensional visualization of micrometer-scale pores and fractures. The Representative Elementary Volume (REV) concept effectively addresses the scale correlation between the heterogeneity of microscopic pores and fractures in coal digital images and macroscopic engineering parameters, with the REV determined collaboratively based on multiple structural parameters being particularly important. Digital images require processing steps such as denoising, threshold segmentation, and three-dimensional reconstruction to effectively observe the pore-fracture structure. In the segmentation process, the MP-Otsu method and the deep learning approach based on U-Net demonstrate significant advantages. Seepage simulation based on three-dimensional reconstruction models from digital images is an effective pathway to reveal the intrinsic mechanisms linking pore-fracture structure and water seepage behavior. Research using controlled methods, such as the digital image artificial fracture technique, indicates that pore-fracture shape is a key factor influencing permeability, with significant differences in the contribution of different shapes. The influence of fracture aperture on seepage exhibits a nonlinear segmented characteristic and produces a coupling effect with surface roughness. Connected pores and fractures are confirmed as the primary channels for water migration, significantly enhancing the understanding of the true state of water distribution within the coal mass. Currently, digital imaging technology still faces key challenges in coal seam water injection seepage research, including the insufficient applicability of existing pore-fracture characterization methods to organic rocks like coal, difficulty in defining the permeability REV, and the contradiction between image resolution and field of view. Future research should focus on developing new in-situ dynamic imaging technologies, establishing multi-scale coupled seepage prediction models, and vigorously advancing multi-scale image fusion and super-resolution reconstruction algorithms based on artificial intelligence to promote the precise and efficient development of coal seam water injection technology.