The dimensions of the photo should be be 256x256 (or very similar) and should be cropped to a square, otherwise the proportions of the photo will skew.
We recommend that you invest a little time in getting the photo’s consistent and looking good; it will make employees feel good. Go for a nice background, well lit. A front-on photo of the employees head and shoulders should work well within the given dimensions.
See the example:
Customer Service Team