using image place holders in a database field?

Hi all, I want to use image place holders in a mysql field. The field will store a newsletter article and I want to include and display an image in the article. For example I will have: "the article text ##image_name## some more article text". I will use str_replace to replace ##image_name## with the html tag to display such as <img src='/images/image_name'>. But - I don't know how to write the str_replace! Can anyone help? Also, is there are better way to do this?? Can I have images displayed in the middle of text from a field some other way? I also cannot seem to find much on using place holders in a field - but I can see it's advantages. I hope this all makes sense... Regards, Matthew Delmarter