When using someone else's words, ideas, charts, images and the like, you have to acknowledge where the information came from. Failure to do so is plagiarism. Using footnotes, bibliographies, in-text citations, and similar strategies serves two main purposes:
You must credit the source of images, figures, charts, tables, etc. that you include in your papers. The formatting style will prescribe whether the source is cited only as part of the caption for the image/table/figure, or in both the caption and the list of references or works cited.
Consult the following for more details and examples of captions and citations for images, tables, figures, etc.: