Counting colonies is traditionally performed manually using a pencil and a click-counter. This is generally a straightforward task but can become very laborious and time consuming when many plates have to be enumerated.
Alternatively, semi-automatic (software) and automatic (hardware + software) solutions can be used.
Colonies can be enumerated from pictures of plates using software tools. The experimenters would generally take a picture of each plate they need to count and then analyze all the pictures (this can be done with a simple digital camera or even a webcam). Since it takes less than 10 seconds to take a single picture, as opposed to several minutes to count CFU manually, this approach generally saves a lot of time. In addition, it is more objective and allows the extraction of other variables such as the size and color of the colonies.