I tried Firebug and at this stage of my working on things, I found it confusing.
So, I deleted my child theme and recreated it. Here's what's in my child theme style.css:
Theme Name: Water Works Conservancy
Description: website to promote the work of an edicational and historic preservation advocacy organization.
(optional values you can add: Theme URI, Author URI, Version)
I have added nothing to the style sheet at this point. Here is the site
As you can see, the graphic is miniaturized. The original graphic that I loaded as header graphic is 1009 x 100.
When I loaded the graphic up, it appeared full size on the screen with a crop box superimposed. I clicked the button that said to ignore the cropping and accept the image as I had loaded it.
So, at this point - at this iteration of my child theme, I have done nothing - no styling at all, no coding at all, and the image appears miniaturized.
I went back to Fire bug and while some of the margin settings I would change, they don't seem to be really affecting what's happening with the image. I changed the column setting to grid_12_of_12, and I saw the box expand, but the image didn't change. I went to the img code and, in the style sheet the controlling sizing is height-auto, width-100%. But that isn't making the graphic it's full size. So something else has to be controlling what happened to the graphic.
Could it bee that whatever process is involved with the header/background/theme options selection is controlling this? I don't see where I have any control over the internal workings of that process.
What do I do now?