The above is a link that explains heat pressing step by step, and printing the image is covered in there. A recap is:
Papers for light/white shirts, you "mirror'' or flip the image.
Papers for darks shirts (called dark or opaque papers) you do NOT mirror the image.
Setting is for Plain Paper setting. Text/normal mode is fine, but folks have said they use photo settings. Photo settings lay more ink on the paper, and that can cause problems like bleeding or running. Too much ink is no good, less is better for this. The ink sits *on top* of the paper, so adding more is no benefit.
As far as images on the net, whoever took the photo or created the image owns the copyright. You can't use others copyrighted images.
You can get photoshop (or gimp, freeware type photoshop software) or coreldraw (or inkscape.org, freeware type of corel software) and create your own images, or join places like clipart.com that has royalty free images for you to use.
There is a thread on here of how to get the 1 yr (normally $129-159) of clipart.com for a few bucks. Look up the thread "clipart free".