The techniques based on fractals show promising results in the field of image understanding and visualization of high complexity data. In the aim to give an introduction to the theory of fractals the following topics will be summarised in this paper: the definition and analysis of fractals based on self-similarity and self-affinity behaviours, definitions for fractal dimension, fractal synthesis, multiresolution approach in the analysis and synthesis of fractals, fractals and hierarchic stochastic processes. The derived techniques with applications in geo-information processing and understanding will be underlined: generation of synthetic DEMs , fractal resampling of actual DEMs, algorithms for computation of the fractal dimension, unknown information modelling and data fusion, multiresolution synthesis and analysis of fractal images, multiresolution analysis and fractal dimension estimation. The paper presents also several experiments using fractals to generate accurate models for landforms and cover types, generation of synthetic images for model based picture processing, and image processing techniques for the analysis of remotely sensed images. The techniques have been applied both for optical and Synthetic Aperture Radar (SAR) image interpretation.