You may have information in form of a picture, but you need numbers. For example, you may have got a gas turbine manufacturers brochure with performance data and you want to model the performance of this engine with GasTurb.
Reading the numbers from such a picture manually is quite time consuming. It is much simpler and quicker with GasTurb Details: Scan the picture and read it as bitmap into GasTurb Details. After setting the scales you can pick numbers from the graphic with mouse button clicks.
The numbers are written to a text file which can be used for any purpose, not only for performance calculations.