You can specify alternative text for pictures in a Microsoft Office InfoPath 2007 form template. Alternative text appears when a user moves the pointer over a picture, and also helps users with screen readers understand the content of pictures.
Right-click the picture, and then click Format Picture on the shortcut menu.
Click the Text tab.
In the Alternative text box, type the text you want.
Tip: The text can be as long as you want, but some Web browsers might be able to display only a limited number of characters.