There are two types of visual art that is put onto the wall, the murals and graffiti. Wall mural art is an image that contains moral message and use watercolor, oil paint or chalk. While graffiti is words that contains particular purpose, it could be protest or secret language of a community, tools that used are spray paint and commonly simply stroked without consideration of the art of drawing.
The difference is these two types of art in addition to media images and words, also on the containing. wall mural art is always conveying information and criticism that can be understood by everyone, while graffiti can be only understood by people in certain groups. Graffiti is more often contains anger while wall mural art although it contains protests and loaded anger but in a more subtle form.
Among these differences there are similarities between the murals and graffiti, that they were both put on the wall and carried out by the community. But sometimes graffiti is personalize and have wild impress, so reaping the protests from the community itself and assumed as vandalism, but it is not meant to be and not all graffiti is so. Positive or negative impression gained by graffiti is depended on the creator.
Image source : houzz