I think the problem with monitoring workers' screens is you are trying to ensure that they are "working". Instead the client should have managers who are trying

I think the problem with monitoring workers' screens is you are trying to ensure that they are "working". Instead the client should have managers who are trying to figure out WHAT the workers are working on. To understand whether useful work is being done you need to understand the structure of the application, and then understand what kind of progress is made in terms of that. Manage the development of the product, not workers' time.