Follow these steps to create Japanese style flower brushes from stock photos
Regardless of the kind of flowers you want to use to make brushes, the actual brush making procedure is exactly the same, and to save you having to paint the footprint for each brush individually, this process start with copying and pasting a source photograph onto a layer above a white background.
With your source image pasted (Edit>Copy on the image, and Edit>Paste on your blank file), choose the Brush Tool and select a small hard brush from the Brush Picker. Now hit Q on the keyboard to enter Quick Mask Mode. Now double-click the Quick Mask icon at the base of the Toolbar and choose a contrasting colour for the mask overlay.
For the “Colour Indicates” option choose Selected Areas and click OK. Ensure that you’re using Black on your brush (check the Foreground Colour swatch) and using the brush at 100% Opacity start to carefully paint over the flower you want to copy.
Take your time with this part of the process, carefully painting over the flower, paying attention to keeping within the flowers outline. If you make a mistake and paint outside of the flowers outline, simply change your Foreground Colour to White and paint back in to the image to hide that part of the mask.
Once your mask is complete, hit Q on the keyboard to exit Quick Mask. With the selection active, go to Edit>Copy followed by Edit>Paste. You can now hide your original image layer. Go to Image>Adjustments>Desaturate. We need to simplify the detail, so go to Filter>Blur>Smart Blur. Use an Amount of 30 for Radius and Threshold and click OK.
Choose the Brush Tool, click in the Brush Picker and load the Wet Media Brushes via the small arrow in the top right. Now select the Rough Ink brush. In the Brushes Palette, choose “Shape Dynamics” and set the Control for Size to Pen Pressure. Ensure your Foreground Colour is Black and add a new layer (Cmd/Ctrl-Shift-N).
Use this brush at a very small size to loosely trace around the flower, using lots of pressure variation. It’s also useful to add a few touches of line within the flowers to add a little detail. When you’re happy, make a rectangular selection around the flower and go to Edit>Define Brush Preset. Give your brush a meaningful name.
To create more brushes, simply use the same procedure over other start images. Now you can use your completed brushes on any image. Either use them in single clicks or use the Jitter values (see the side tip) within the brushes palette to apply many flowers with single strokes.