Psychology test stimuli recommended shapes
If your goal is to find a set of shapes that are unique and easily distinguishable from each other, you might be interested in stimuli that get used in visual statistical learning experiments (e.g. Fiser &amp; Aslin, 2002; Turk-Browne, Junge, &amp; Scholl, 2005). The same set of shapes tends to get used across multiple studies in this literature. Some examples of these shapes:





There is a repository of some of these shapes on GitHub. You can download the images there.

Note that there hasn't been research on these shapes, just that they are commonly used shapes in the literature when arbitrary 2D shapes are needed. It is likely that some pairs of these shapes are more similar than others, but since there are a couple dozen different shapes, you may be able to control for that by randomly selecting a different subset of the shapes for each subject in the experiment.