The first of the three elements, explain the action, is the most important part of the caption. The very first sentence must link the caption to the photograph by describing the action. One of the peculiarities of the first sentence in caption writing is its verb form. Since a photograph has frozen a moment in time, the verb should be written in present tense. This provides a sense of immediacy, as though the reader is actually witnessing the event. For example:

"Petty Officer Second Class Paul T. Boat swims through swirling flood waters of the St. Johns River to rescue 6-year-old Sammy Cameron . . . ."

This has more dramatic impact than a caption which reads:

"Petty Officer Second Class Jane B. Doe swam through . . . ."

There is, however, one problem that arises from the use of present tense in the first sentence. What to do with the when or time element? If the when or time element is included in the first sentence, the result reads something like this:

Pete Rose hit a line drive to center field yesterday . . . .

A sentence, such as this, would be somewhat jarring to the reader and should be avoided. To alleviate the problem, you should leave out the when or time element of the first sentence when writing captions, thus avoiding an awkward shift in tense.