Create a PNG from a set background and embed a personalisation

I am after someone to set up a program where I have a set background image but then it creates a PNG file which has a personalised to it.
For example, the link here goes to a square with a background, and then it has a number plate (in the UK Number Plate font) with 786 in it.
https://www.primoregistrations.co.uk/media/images/google/786.png
I am after the 786 being embedded on the PNG by the variable on the end of the hyperlink so if I put 911 in then it will show 911 instead of 786 etc.