The words and logos are called watermarking. It is used to protect your photos from being posted on someone elses website and also so that if someone finds a picture of your cake somewhere they can identify who made it (advertising).
You can get some sample watermarking programs here.
http://cameras.about.com/od/printing/ss/watermark_2.htm
i am not sure about a program for a black background, but i use picnik, it is a free website for photo editing. I love it, so easy and quick to use!
It's easier to get a solid-colored background by taking a picture of the cake on one...lay the fabric out, set the cake on it, then have someone hold the fabric up or drape it on the chair back or pin it to the wall, depending on where your cake is, and then you can get a picture with a solid-color background with no crease.
Most photos of food look better if they've been cleaned up a little bit with photo editing software. I use Paint Shop Pro because it's easy and cheaper than photoshop (besides I'm a bad girl and didn't exactly pay for it 
)
Here's one that I edited, with the original beside it. I take pictures with my phone right now because I'm having camera issues, and my originals are usually terrible.
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