We address the problem of zero-order-free image reconstruction in digital holographic microscopy. We show how the goal can be achieved by confining the object-wave modulation to one quadrant of the frequency domain, and by maintaining a reference-wave intensity higher than that of the object. The proposed technique is nonlinear, noniterative, and leads to exact reconstruction in the absence of noise. We also provide experimental results on holograms of yew pollen grains to validate the theoretical results.