Question: I would like to change the image next to the search box to a styled input button.

Do I need to create a new delegate control to do this? Can I do this with css, if so how?

This is the standard search UI  

![enter image description here](https://i.stack.imgur.com/bRp3m.jpg)

This is the desired css button look  

![enter image description here](https://i.stack.imgur.com/t59MW.jpg)

Answer: 
The image is rendered using an tag which you cannot modify using just CSS. You could either

* A - Use some jQuery to modify the HTML for the searchbox. You can target the srch-gosearchimg CSS class to modify the image tag and point it to another source image.
* B - Use a delegate control to replace the entire searchbox

My vote usually goes for option B since I don't like messing with a non-standardized HTML layout that jQuery uses. E.g. if a service pack is installed which changes the default searchbox then it'll blow your jquery out of the water. For option B you do need to have server access. For option A you do not since you can include jQuery using a content editor part or in the masterpage using SharePoint Designer.
Just throwing this into the discussion...
Erik Swenson did 2 great blog posts regarding how to change the way the OOTB search box looks like:
<http://erikswenson.blogspot.com/2011/02/sharepoint-2010-large-search-box-scopes.html>
and
<http://erikswenson.blogspot.com/2011/02/sharepoint-2010-large-search-box.html>
Seems to me that reusing the default control and changing the default image/ icon via css would be the easiest solution?
Greg