"Hey, you can paint so good. Can you maybe paint me a car? How about the new Audi R8 coupe in blue?"
Me: "Uh ... nope."
This is similar to the sound of acquaintances who believe that because I can paint something well, I can immediately paint ANYTHING super. Not everyone can paint a car instantly, not to mention a specific brand or type of car. But that's not because I can't paint, it's because I don't have a picture in mind to guide me. In other words, my visual library is missing the drawer for cars. What this means exactly, I'll explain to you in just now.
The "Rhinocerus" by Albrecht Dürer
A famous example on the topic of "visual library" is the picture of the "Rhinocerus" by Albrecht Dürer. Back in 16th century Europe, exotic animals like the rhinoceros or the elephant were true rarities. Nobody knew what such an animal looked like. When a specimen of an armored rhinoceros appeared in Lisbon in 1515, it fascinated people so much that even Albrecht Dürer in faraway Nuremberg felt called to draw the animal so that he could then sell the woodcut prints to the people. The problem, of course, was that good Albrecht had never seen a tank rhinoceros. Only through a sketch by an unknown artist and through other people's descriptions could he get a picture of it. The result, of course, was far from realistic. Dürer simply lacked the experience of having seen a rhinoceros.
The visual library
Every person has lived through different things and had different experiences. A person who has never seen a certain thing will, of course, never be able to represent that thing correctly (as Dürer has done with his "Rhinocerus"). That's why, as an artist, it's very important to study the subject you want to paint. It is often the case that you start a painting without any preparation at all, but the probability that mistakes will creep in will then be greater than if you have dealt with the objects beforehand. So before you start a painting, you need to know what you want to paint in the first place ... and start only then.
Every time I want to paint a picture and I can't imagine what an object looks like, I go on the net and browse all the sites for suitable objects. For example, the picture of Lara Croft that I painted as part of a Tomb Raider contest: Of course I knew Tomb Raider and had a rough picture of Lara in my head, but I didn't know the finer details. Mainly because today's younger Lara Croft looks different. To expand my visual library, I tried to collect all the images. I collected pictures of Lara Croft, guns, Japanese plane wrecks, rocks, etc. and put them in folders. Then I looked at them carefully and studied them in order to approach my image with the correct idea in my head.
A gun is not just a gun
With this painting, I realized pretty quickly that I couldn't paint guns. I knew what a gun looked like, but I didn't know the details and proportions. This was because I had never painted a gun before. By having a small collection of pictures, I was able to make comparisons and later paint the gun myself. It was like painting a picture within a picture. For this gun, I had to create a technical drawing to represent everything correctly. I gained valuable experience from this action and expanded my visual library. The next time if I want to paint a gun, I'll know better what to look for.
How do I expand my visual library?
I think it's obvious that each of us can gain a lot of experience through study drawings. Anything we draw once will come easier to us when we draw it again. Creating a collection of images is also a good idea; it can save us time and we don't have to search again. Google search is of course a good helper, but when it comes to images, I rather recommend Pinterest or image databases like Getty or iStockphoto. There you can find a better selection of images.
Lastly, I would like to recommend one simple thing: Just keep your eyes open. Observe things, try to understand and capture them. It's not enough to just look for pictures of something and paint them off. Especially with things that you can't represent so well on photos, like water or light. You will rarely find a suitable photo of a light source or of reflections - these are things you have to understand. Only when you understand them will you keep them in your visual library.