I always add credits to the bottom of my page if I use someone else's work in my headers. I don't if it's entirely from things I created.
This brings me to a question that has been asked a few times, where to find the flowers I used in my avatar, and eventually in the matching header I just created today.
You can find the entire kit, a charity compilation from many designers, over at Scrapbook-Bytes.
Note that I recolored the blue flower to get the pink and yellow. Only a blue, green and white flower are included in the kit called "Ethan Charles".
I do create blog headers and avatars (but not for free, though I do barter if someone is low on cash). The cost does include help uploading it to your blog. For info on that just send me an email.