Thanks. I double-checked and we are in the correct template. Below is the small portion of code that seems to control the image. I am not sure what to do to replace this image with our own copy, which is the welcome.txt file.
<div class="welcome-top">
<img src="{$AltImagesDir}/fashion_mosaic/welcome.jpg" class="welcome" alt="" />
{if $categories_menu_list}
{$lng.txt_welcome class="welcome"}
{include file="customer/categories.tpl"}
{else}
<img src="{$ImagesDir}/spacer.gif" alt="" class="empty-height-extender" />
{/if}
</div>