You can apply masking/filtering to image files.
Masking is useful for cropping a specific area of an image. You can select a masking type among ‘circle’, ‘rect’, ‘gauss’, and ‘manual’. Filtering is useful for, for example, blurring an image. Filtering is not a feature of the psychophysics plugin, but rather an experimental feature provided by canvas. For more information, please check this page.
See the image section of Stimulus parameters to learn how to apply masking/filtering the image.
See also the demos/mask_filter.html.