First open your nice new pic you've just found...(this can be replaced with any image)
As its a piece of lace its white and on this occasion just happens to be on a black background...which is perfect for what we want to create.
If you're using a pic that isnt black and white just make it greyscale to use as a brush.
In photoshop when creating a brush....anything thats white is viewed as transparent and anything black is opaque, with greyscales being viewed as translucent.
So to have the lace as the actual brush we have to invert the pic....so the lace appears black and the white background will vanish.
now to turn it into a custom brush just click edit/define brush preset
then give the brush a name
The brush will be auto saved in the brush folder
Its that simple.
Heres how our custom made brush looks when white has been selected as the brush colour and the background layer set as pink so the brush stroke can be seen.
For paint.net users....download the custom brush plug in and save and intended brush as a png in the brushes folder(making sure to delete the background you dont need before saving).
To use photoshop brushes in paint.net then you can download a conversion tool that lets you convert .abr format brushes into .png so paint.net can use them.....you can get that here http://sourceforge.net/projects/abrviewer/
For Gimp users save the inverted image as a .gbr in the brushes directory of your application
If you think of modifying/reusing the elements of your image later on, it is the moment to save now as .xcf or never come back : the creation of the brush is an operation with a single direction. Once the file ".gbr" is generated, one loses the original elements of the work in progress.
Commentary by bi_bi_love
1 point to note - in GIMP you will need to create your brush on a transparent layer, similar to when you create clothes or open a new image as a transparency as GIMP does not automatically see white as transparent.
So using Sarah's pictures, open a new image [File-New...] and create a new transparent layer [Layer-New Layer... or the method I used in my clothing tutorial].
Once you have inverted the colours [Colors-Invert], use the colour selection tool and select the bordering colour (now white) and use Threshold slider to get it as fine as possible. Then delete the selection.
Hide the background layer and so you only have the image you want sat on the dark and light grey transparency background.
Use the rectangle selcet tool and get it in as close to the edge of your image as possible then crop to selection [Image-Crop to selection]
Using exactly the same technique you can create patterns in GIMP...follow all the steps and save the the finished file to the Patterns folder with the .pat extension. You may want to consider the size that you resize to before saving so it will be in good relation to the size of the images you will probably use it on.
The location of the folders should be something like -
XP
Documents and Settings-<user>-GIMP 2.x
Vista or W7
Users-<user>-GIMP 2.x