Unless you put the picture in the Background (Format/Sheet/Background),
in which case it will be tiled throughout the entire sheet, you can't
directly type over a picture because pictures "live" in the Drawing
layer above the cells.

You can make the picture transparent (Format/Picture) to see text in the
cells beneath.

You can also use the Camera Tool to create a linked picture of a cell
and position it on top of the other picture. Set the Fill to No fill,
and the border to No Line.