This is neither novel, nor morally acceptable. People that do this work usually end up traumatized for life, because of the fucked up shit they often have to look at. Prisoners are not really in a position to negotiate, meaning you can push this work on them in a sort of non consentual way that is below what modern society should strive for.
Unfortunately one major sector of image machine learning is CSAM scanning, which was also recently revealed as one of the major funding parties for the planned legislation intended to allow scanning all private communication in the EU. But generally i agree most of the things they will see might not be too bad by themselves but its still a job no human really wants to do of their own free will. If they do decide to do it, it is either out of a lack of choice or because they dont know what they are getting themselves into.
Prisoners are not really in a position to negotiate, meaning you can push this work on them in a sort of non consentual way that is below what modern society should strive for
Well the article does mention that the prisoner "Marmalade" was not forced to do any of this.
In fact the article mentions that she could have spend her time in her cell, doing online courses or doing chores for the prison for little cash. The fact that wired managed to just book an interview with the prisoner also makes it quite risky for the company to subject the prisoners to any traumatizing material.
The only problem I really see with this is the fact that this doesn't really prepare the prisoners for live outside the prison in any way.
Forgive me for not trusting in the investigative journalism capabilities of fucking "wired". How much of a choice that person really had is not something u can judge from an outside perspective. If they made this the highest paying jobs then there is no real choice probably.
We can make fairly accurate assumptions on prisoners rights simply based on the fact that the prison is located in Finland.
Here's article from Yle (one of the most trusted news organizations in Finland) describing finnish prisons.