HOW SET IMAGES FOR IMPORTING

Hi
I need the shape of a number (the 25).
All the words have to be written inside the numbers.
Since in the default shapes I didn't find numbers, I've thought to create in in Photoshop and then import.
The qeustion is: how can I make understand the algorytm that the part to be written in are the numbers? have I to color them in a specific colour? And the file that will be imported, has to be jpg or some other extension?

In general words are placed on non-white space so making the numbers any non-white color will work.

Use JPG or PNG extension for your image file.