Quote - If I understand the whole thing correctly: Yes.
I used the image (sunset) I had, doubled the canvas width, mirrored the sunset, then increased the height, filling the bottom 48% of the image with black. Overall size of the image used was about 6000X4000 pixels.
When it asked if I wanted to have lighting calculated automatically, I clicked yes.
Since this image, I've rendered a skydome without any objects present, then re-inserted it into the atmosphere environment and am rendering it again  

Technically you are using an LDRI and if it is a simple photo then it is really Low, but I would rather use a Really High Res-LDRI, I know that sounds like an oxymoron but it's not, rather than a Poorly Constructed HDRI. I use very large Panos, some 180s some 360s and get some very effective results. That Tut that Paul sent above is good one if you want to make HDRIs from your Photos. You can also use HDRI Shop LINK You can download version 1 for Free but V2 will cost you a little. I have V1 but have never used it cause I have almost 150 LDRIs and over 180 HDRIs of which I paid for only 30 of and the rest were free on the Internet.

I would rather be Politically Incorrect,
Then have Politically Correct-Incorrectness!!!