The search to directly image and characterize exoplanets that are initially hidden below the stellar and instrumental noise relies on the use of both extreme adaptive optics (AO) and a subsequent point spread function (PSF) subtraction pipeline. In this thesis I present my research on both real-time AO techniques and post-processing PSF subtraction techniques. First, I present a new PSF subtraction algorithm designed to image the HR 8799 debris disk using the Hubble Space Telescope. I find an over-luminosity after PSF subtraction that may be from the inner disk and/or planetesimal belt components of this system, but ultimately conclude that this is likely a non-detection as a result of telescope stability and broadband chromatic effects. Thus, assuming a non-detection, I derive upper limits on the HR 8799 dust belt mass in small grains, consistent with measurements of other debris disk halos. This important result suggests that a detection may not be possible until the rise of future, more stable space telescopes. Next, I present a new PSF subtraction algorithm applied to current campaign data from the Gemini Planet Imager (GPI), designed to optimize the GPI planet detection sensitivity of narrow orbit planets. My results, while still being investigated, seem to show that current algorithms are already optimized, and that limited gains can be achieved with my new algorithm. Finally, I apply a new real-time AO nulling technique, called super-Nyquist wavefront control (SNWFC), to be used on future 30 m class telescopes to image wide-orbit exoplanets. I demonstrate application of SNWFC in both a deterministic laboratory experiment and coronagraphic simulations using an interferometric nulling technique, suggesting that this technique would allow higher SNR characterization of wide-orbit exoplanets on future telescopes.