This script is an extension of the "Click on an image to record (x,y) points" from the Data Table Tools Add-in by Brady Brady, JMP Division, SAS. It approximates the graph as a density so Distribution - Continous fit can convert it to an equation.
Choose a sketch of a probability function or blank grid.
Fill frame and set the x and y scales (e.g. 0,0 & 10,10).
Add points to approximate the desired probability function.
Press the close button...
(Fit Spline [Lambda 0.05] and save prediction formula).
(Exclude original data, add 200 rows incrementing X from its smallest to largest values)
(Normalise the generated predicted Y's and convert to a count such that the total count ~10,000)
(Create a new table with each increment of X duplicated the number of times indicated by step 6)
(Run Fit Continuous - All in the Distribution platform)
Choose the closest function with the correct properties and make a note of the hyperparameters.
Optional (JMP Pro): Use bootstrap to get an idea of the ranges the hyperparameters might take.