Luckily I do not have half a brain, so let me try to help you. Yes these brushes are images, but I suppose the Watercolor brushes in Illustrator started out that way. Have a look at the brushes that are part of Illustrator: Brushes Panel > Open Brush Library > Artistic > Artistic Watercolor Drag them from the Brushes panel to your artboard to see what they contain. Most of them are groups with reduced opacity. Double click them in the Brushes Panel to see their options. Learn how to create them from scanned brush strokes with Image Trace and shades of gray. Be careful when using them, the resulting file can become very complex and will sometimes only print if you create a rasterised version,
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