The img tag will include an image in the text. It is considered equivalent to a paragraph tag. The required attribute file can be used to search to specify the filename. What kind of file is used depends on the output format. Normally, using png images should work with all output formats.
The caption attribute is optional and can be used to specify a caption text which will be displayed above or under the figure. Lastly, the name attribute can be used to attach a name to the figure (a label to which can be referred).
See also: p (165).