These are a jpeg and a png image created dynamically by my plotter. The tool knows many interesting functions used in mathematics, statistics and even physics, can draw images of their curves on demand and calculate tables of function values (there's a latex tabular format).
Why and how
plotter was created because I'm lazy - I wanted the possibility to do quick and (more or less) painless plots of functions to use in some advanced maths lectures.
To run a plotter, a webserver with PHP >= 4.3 and an enabled GD-Extension is required.