Waste pickers in the clothing canyons of Ghana, or any other landfill/wasteland
Volunteer caregivers for people with disabilities, especially in places where there are limited or no social safety nets
Street vendors like the children hawking goods in Yemen or Samoa or Zimbabwe...
Cleaners, such as the Sewer divers in places like India where there is no protective equipment provided
Food services workers.
"Domestic" services workers like childcare, housekeeping, etc. I include victims of forced marriages here.
All other exploited, outsourced, trafficked, and/or forced labour, such as the cobalt miners in Congo, or the clothing sweatshop workers in Bangladesh, or the Phillipines call centre workers, or the hazelnut pickers in Turkey, or construction labourers in Qatar, or the chaingangs in the US.
Sudharak Olwe has spent a lot of time documenting the lives of "conservancy workers" in Mumbai. His entire body of work is worth a look, Content warning: Image 12 is extremely NSFL with the body of a human child, but there are also dead and dying animals in images 4 and 11but here is one collection. The photo I see most frequently is the one of a worker neck-deep in a drain