Modified theme images aren’t loading

I’d like some hints about background images in themes – I want to modify the image at the top of the sidebar in my theme (fervens-a) but I can’t get it to work. (Sorry if this is a really simple question – I know some CSS but I’m not an expert).

I have tried modifying the image (just changing the colour) and loading it under the same name in the images folder. Even after emptying the cache and forcing reload several times it still shows the old image. When I get it from the server it is clearly the new colour, but it is the old one that is being loaded.

I have also tried changing the path in the stylesheet, as it was as if it wasn’t loading the images from where I think they were at all, but an absolute path made no difference.

I even tried deleting the entire images folder from the server, but the images still load! Even after emptying the cache and forcing reloads. If I alter the stylesheet with the wrong path to the image, the images don’t load at all. But with the right path to a non-existing images folder, they do! Confused!

Help please! What am I missing? Here is the relevant code for the sidebar search panel:

/* Search Panel
+++++++++++++++++++++++++++++++++++++++++++++++++ */
.s2 .search { background: #4a7e00 url(images/search-top.png) no-repeat top; width: 270px; padding: 7px 15px 10px 15px;}
.s2 .search h3 { padding-bottom: 15px; background: none; padding-left: 0px;}
.s2 .search input { border: none; background: url(images/search-form.png) no-repeat; padding: 7px 10px 7px 10px; font: normal 12px/14px 'Verdana'; color:#fff;}
.s2 .search button { background: none; border: none; padding: 0px; margin: 0px; width: 58px; height: 26px;}

It is the search-top.png I’ve been trying to modify, using Pixelmator. Is the image wrongly compressed? Is this not the code that I need to change? Is there a style override somewhere that I am missing? Does WordPress cache images in some way that I don’t know about? I’d be really grateful for any tips as I am tearing my hair out!

Thanks heaps!