This thesis describes a system, Sysifos, that automates capturing and segmentation of screen dumpsof web pages. The system builds a model of the spatial structure of a page based on the segmentation.The model is used when comparing two screen dumps. The system uses image analysis techniques tosegment the page. The model is then compared to a model generated earlier. The model comparisonis packaged in a form so that it may be used as a test oracle in standard Java testing frameworks, forexample Junit or TestnG. The motivation for the development of Sysifos is that there are currently noestablished ways to automate testing of browser rendering, although browser related bugs are impor-tant. In this thesis one operation running 56 high volume websites was investigated, and it was foundthat browser related bugs represented around 13% of all bugs needing developer attention. Sysifoswas evaluated using a test set containing known errors. It found 100% of the errors it was expected toﬁnd, but reported one false positive. Test results are visualized using SVG. This thesis show that usinga test oracle may be beneﬁcial when testing browser rendering of web pages. Currently, the imagecapturing service of Sysifos is not satisfactory according to speed and reliability, but the results ofthe evaluation indicate that Sysifos has the potential to become a valuable tool if the image capturingservice can be improved.