So here is how to increase the file size of any image file (in fact any type of file):
As you can see from the screenshot above we have a 28 KB image. By going to its properties (right click on it) we can add some text in comments box without any effect on the picture quality.
After this operation our image size increased to 32 KB from 28 KB. We haven’t changed anything else.
Increase rate is proportional to text length, if you want to have a bigger increase insert longer text.