This is a complement to our previous post The Ultimative Guide For the_post_thumbnail In WordPress 2.9. In WordPress Version 2.9 probably the most discussed feature is the post thumbnail. Important for this function, it is only working when it is explicitly enabled in the theme. This can be done with the following little snippet in the functions.php of the theme:
But even with this feature you should check for the existence of the function and offer an alternative. Only then you can leave the user the freedom to choose which WordPress version he wants to use. The functions of extensions, plugins and themes should be checked for their existence, then the functionality of the theme is secured, even if a function is not available. Similarly should it be handled with post thumbnail.
I would like to show two suggestions for alternatives below, and I refer to the detailed article about the topic images in Easier And Better Solutions To Get Pictures On Your Posts.