My understanding is that you define a pool of tasks and users "solve them".
I am looking at a slightly different use case with more open-ended tasks. For instance, we would like users to create an inventory of AED devices (automated external defibrillator) available in a given neighborhood. See http://www.irescu.info/ .
The task would be to create a new entry for each AED device they find.
Could pyBossa be used for such tasks?
PYBOSSA is not designed for such scenarios, however PYBOSSA is integrated with EpiCollect+ a software that allows users to report via their phone exactly what you want. Then, if you need to, you can import the data (photo, GPS location of the device, etc.) into a PYBOSSA server so other users can validate the information (if you need to).
An example of this approach is our Crowdcrafting project: http://crowdcrafting.org/project/airquality
This project uses EpiCollect+ to take photos of lichens, and then we use PYBOSSA to measure the area the cover so we can quantify the quality of the air (there's a link between the area that a lichen covers and the quality of the air, you have all the details in the project page). Thus, while PYBOSSA is not designed for this specific task, its integrations allow you to achieve what you want.