Instead of applying an effect to an entire image or to a selected area, you can opt to "brush in" an effect using the History brush. You have absolute control with respect to the brush size and the opacity of the effect and can create great effects using any of the built-in and plug-in filters available with Photoshop.
Open the File
Choose File, Open and select the file you want to modify.
Apply a Filter
Apply any of Photoshop's filters to create a desired effect. In this example, we applied the Graphic Pen filter to the image.
Open the History Palette
Choose Window, History to open the History palette. Click the snapshot at the top of the palette to revert the image to its previous state. The state reflecting the filter application is still in the History palette but is grayed out. When you start with the History "snapshot," you have something (an effect) to brush back into the photograph.
Set the History Source
Click in the column to the left of the filter state you applied in Step 2 to set the History brush source for the filter effect. In this example, we are setting the History brush so that it will paint in the Graphic Pen filter.
Set History Brush Options
In the Options bar, set the Opacity as desired and choose a brush size from the Brushes section.
Paint the Effect
Move the cursor into the image and paint with the History brush to selectively brush in the filter effect. In this example, we paint the Graphic Pen filter over the background to give it a more textured appearance.
Applying More Than One Filter
To paint from more than one filter source, apply multiple filters and save a snapshot of each one in the History palette. To save a snapshot, choose New Snapshot from the History palette menu when the filter effect is active. Set the History brush source to the desired snapshot to paint with a specific filter effect.