How you cite an image will depend on the citation style you are using. Commonly, image citations should include:
A Digital Object Identifier, or DOI, is a specific code assigned to individual articles. DOIs provide a permanent path to the resource. They are commonly used by publishers and usually look something like this, doi:10.1016/j.foreco.2009.01.017
Due to their ability to provide direct access to articles, many citation formats require you to include the DOI in your citation. Here is an example of a citation in APA including a DOI:
J.A. Gravelle, G. Ice, T.E. Link, D.L. Cook, Nutrient concentration dynamics in an inland Pacific Northwest watershed before and after timber harvest, Forest Ecology and Management, Volume 257 (8), 1663-1675. doi:10.1016/j.foreco.2009.01.017
Data citation allows for discoverability and reuse of research data. It also allows for attribution and tracking of use to better measure the impact of a dataset which in turn promotes better science.
If you are following a particular style, try to form the citation according to the general rules of that style. If in doubt, it is better to provide more information than less.
The main parts of a data citation are: