If saving brushes is similar to that of Photoshop this might work for that as well.

Have you ever wanted to make your own brushes because all others suck? Here's how.

I'm writing this as I'm doing it for the first time; I'm sure it works.

First get your camera, yes your camera. Typically you should do this at night; you'll see why. If you have a terrible nightshot mode, switch to that and point the camera at a light. Hit the "take picture" button and if your camera is like mine it'll go nuts with the focusing; while it's doing that move the camera around in circles or whatever you want the brushes to look like. Again, this should be done in the dark.

Sounds crazy doesn't it? Well take a look at the results; you should have a image of nothing but a bunch of lights, like this:



That's what some ignorant people would call a ghost, but my "ghost" is going to be a GIMP brush; wouldn't some of the spots in there look cool as one? My target areas are going to be in between the 2 circles in the left and the middle. They look fractal-brush-ish yes?


Go to GIMP, open the image you want to make a brush. Here's my targer area for this:



That will be my brush. Click the rectangular-selection tool (Press R in Gimp) and drag, on the image, what areas you want to make the brush. I already did that in the above image.

Now right click it and go to Edit>Copy.
Go to File>New and just click OK. GIMP automatically resizes the default-size window to suit what you copied. Now Edit>Paste. You should have this:


HAY MY POST IS IN THE BACKGROUND HEY WOOO GO ME

Go to Layer>Colors>Desasturate. This makes the image black & white which is what you want.

Go to File>Save and click "Select File Type". Scroll down until you see "GIMP Brush" and select that, then click Save. Just click OK at the next window that comes up. If this setting doesn't work, like it didn't for me, go to "GIMP Brush (animated)" instead.

Now put the file wherever you keep your GIMP brushes, and give it a name you'll recognize. Me? "Untitled" :)
Now restart GIMP, open a new image and select that brush and try it out.

NOTE: It renamed, for me, the brush to "GIMP Brush Pipe". If you cant see the brush there just click the brushes icon, and go to "Open brush selection dialog" which is the little paintbrush in the bottom right. Makes it easier.

Here's my result with the ONE brush I made; you can make sets and I recommend you do. This is only an example, I'm too lazy right now to make a full set:



But you get the idea.
You can also do this method with other images like clouds or trees, you're not limited to what I did, I only did it like this because it's very easy to throw a camera around in nightshot and get a image like that. And it takes time to cut out the clouds/trees perfectly.

Thanks for trying/reading, please post your results.