If I see a rendering of something, and I try my best to duplicate it, is it stealing? To be more precise, I saw a bubble I liked on Google images, and I tried to duplicate it, for a brush, and did so. It isn't exact, but it's close. Is this stealing?

My personal opinion is that if it's something generic, like a bubble and as long as it's not an exact duplicate, I think it would be OK. Take for example, Wilber or Tux, which are under GPL. There is no reason I can't create my own version of those two designs. I don't consider that stealing.

Forging specific copyrighted artwork is a different matter.

It's not exact, but it's dang close, haha. Took me awhile to do it.

Depends on why you are duplicating it. For example, my signature is a recreation of the tron legacy style which is owned by Disney. I can't sell it. I can't even claim it's mine. I can't make any money off of it or use it to advertise things I do make money from. But they'd be hard-pressed to actually sue me for copyright infringement for a forum sig.

My view on the matter is that as long as you are not using the image for profit then it should be fine. If you do then you should include the original authors name.This way if there is a discrepancy you have a good legal argument.

Consider the type face you use also.
Most folks do not read the README included with a font download but they should if they plan on using it for more than private or non commercial use.

Here is something to ponder. What if say you and i make a bubble with the "Soap Bubble" script and just use default settings. The images are identical. You post yours first as a brush.I post mine as an image.
Does that mean we need to assume you have legal rights to the brush, and image?

Most lawyers will tell you unless there is a specific license saying you can not use it for commercial reasons, assume that you can.