This thesis explores possible improvements, using parallel computing, to the PSF-alignment and image subtraction algorithm found in HOTPANTS. In time-domain astronomy the PSF-alignment and image subtraction algorithm OIS is used to identify transient events. hotpants is a software package based on OIS, the software package ISIS, and other subsequent research done to improve OIS. A parallel GPU implementation of the algorithm from HOTPANTS – henceforth known as BACH –was created for this thesis. The goal of this thesis is to answer the questions: “what parts of HOTPANTS are most suited for parallelisation?” and “how does bach perform compared to HOTPANTS and SFFT?”, another PSF-alignment and image subtraction tool. The authors found that the parts most susceptible to parallelisation were the convolution and subtraction steps. However, the subtraction did not display a significant improvement to its sequential counterpart. The other parts of HOTPANTS were deemed too complex to implement in parallel on the GPU. However, some parts could probably either be partly parallelised on the GPU or parallelised usingthe CPU. BACH was always as fast as or faster than HOTPANTS; it was generally 2 times faster, but was up to 4.5 times faster in some test cases. It was also faster than SFFT, but this result was not equivalent to the result presented in [15], which is why the authors of this thesis believe something was wrong with either the installation of SFFT or the hardware used to test it.