The cover sells the book.
This is undoubtedly true. So in addition to well-written, carefully edited content, now you need to find a cover. One option is to buy one. There is only one problem with that, and if you're an "emerging emerging" authoress, it's a doozy. Paying $25-$50 for an inexpensive cover may put the book into negative profits for a long time. Especially if you're using low cost or free to build an audience. The only viable option is to do it yourself. Mine aren't too bad, so I thought I'd show you how I do it.
1) Image sources. For regency romances, Wikimedia is fantastic. The Getty and the USA national gallery are also good. The google art project works. Even using a websearch directly will work.
Make sure that the images are public domain and do your best to comply with the source's attribution requirements.
It is important to pick an image with sufficient quality to reproduce well, and this can be a real difficulty. A small amount of scaling can be improved using the GIMP and unsharp masking, but don't count on correcting a truly marginal image.
I considered using one of Angelina Catalini for a cover. This image shows the original copy. It is not useful.
After hunting around for a while I found a much better copy which could just be used. She has a bit of a daft look, so I decided not to use it in the end.
3) You don't need to tell the whole story in the cover. While it should be related to the story, it is meant to tempt the reader into actually looking at the content, not tell the story. "What about Cecelia?" is set in the country, there's a lot about horses and a dog is actually an important character. (you'll have to read the book to see about that). Notice that the cover doesn't have either a horse or a dog on it.
5) Don't crowd the lettering. The cover above was done with the Gimp. I used layers where the image was in one layer above a black rectangle. The writing was then done on the open area. Both Createspace and Kindle publishing have cover creators that are not too bad. Neither gives you the freedom that rolling your own with an image editing tool has.
6) Technical issues. Oversample by 2-3 times and then reduce. In other words if the final image is 1000x1600 (Kindle size) work at least at 2000x3200. I save a copy both in the Gimp's internal format and as a high-quality JPEG.