Identify the main subjects in the picture. Accurately name the subjects while avoiding to describe the obvious. For example, avoid stating that someone is eating or walking a dog when it is apparent in the picture. Double-check to make sure the names are spelled correctly. Also, include the location and the date if the image is a historic photo or painting. Write the caption in the present tense since the picture captures a specific moment in time.
Choose a specific style. Write either complete sentences or headlines. For example, you can choose to write "The First Lady works with a group of students in the White House garden." or "First Lady works with group of students in White House garden". You can also choose to be very specific when describing a photo, using expressions such as "from left," "in the center" or "standing on the right." You may decide to leave out those phrases and let the reader figure out the direction.
Connect the caption to the story and provide context when necessary. For example: "The First Lady works with a group of students in the White House garden" is sufficient for the story. However, when you add "For the launch of her 'Let's Move' campaign, the First lady works with a group of students in the White House garden," -- it gives context to the image by explaining what happens before and after the photo. It also makes the reader interested in the campaign.
Choose a type that contrasts with the rest of the article. The type can be larger than the article body. It can also be bold or italics. All the different types you use in the article should flow smoothly and complement each other.