Figure/ground ambiguity exists when it is impossible to determine what would be considered figure and what would be considered ground. Common causes of figure/ground ambiguity are blurriness (gradients, camera blur, depth of field, smudging, etc.) or an immense quantity and complexity of figures. When it becomes difficult or impossible to determine when a figure stops and the ground begins, figure/ground ambiguity occurs. Note: this is distinctly different that figure/ground reversal.

Areas of figure/ground ambiguity… figures become indeterminate

Almost entirely figure/ground ambiguous
(figure can be determined along the bottom edge of the image)

Jackson Pollock. Lavender Mist: Number 1. 1950.