To address the difficulties involving algebraic knowledge, such as equations and systems of equations, it is important that studies and research be developed to propose ways to support the teaching and learning of Algebra and Mathematics. One of the difficulties is related to language, and the use of images can be a resource to facilitate the understanding of algebraic language. However, it is necessary for visual language to be supported by theories that can justify its use. Given the above, this work aims to present and highlight Multiple Representations, the Theory of Semiotic Representation Registers, and Contextualization as theoretical foundations for the use of visual language in the teaching and learning of mathematics and systems of equations. To achieve this, four chapters are developed, presenting, discussing, and interweaving these theories with visual language. Finally, it is inferred that these theories provide a foundation for the use of visual language in the teaching and learning of equations and systems of equations, where images can be valuable resources for learning Algebra and understanding algebraic concepts such as unknowns and variables.