Text on centrally aligned image

Hi
I am new to css. I am stuck due to one problem in designing the web page. I align an image in the center of page horizontly. Then I try to write something on that image. But as soon as I write on the image; alignment of image changes automatically to the left side. I did lots of attempts but in vein. I know its very small issue but even then I am unable to finish this task. Can anybody give some valueable suggestions in this regard, please?