Annotate Excel pictures and graphs
 
To add a text to a picture or graph that moves with the object you can use a textbox. Often it is nice to be able to e.g. add a text to the bottom of an image annotating it with a title e.g. Figure  123: title.
 
To do this display the drawing toolbar (view / toolbars / drawing) and choose the textbox object. Type the text.
To fix the textbox to your graph, select both the graph and the textbox. Right click and use the grouping option to group the two together.