This is one of a set of three more images, showing an inner cheek cell stained with methylene blue and imaged with a 40x objective and a RaspberryPi camera in the open public lab, Hackuarium. The cell has a micronucleus (arrow), which is a sign that a large piece of DNA broke of a chromosome in a previous cell division. This cell also has an ambiguous spot (arrow with question mark) which could confusion interpretation.  The micronucleus assay is a classic test (from the 1980s) used for risk assessment of occupational hazards. Segmentation of such images to allow future algorithms to detect a micronucleus automatically is the aim of 'mask-making' as shown in the panel on the right.
<a href="//commons.wikimedia.org/wiki/User:Genomicintegrity" title="User:Genomicintegrity">Genomicintegrity</a>
CC BY 4.0
<span class="int-own-work" lang="en">Own work</span>