Tutorial : Stock images in combination with other pictures

I wrote this tutorial for my friends and posted it here, but since this is actually my first tutorial ever I thought I might as well cross-post to icon_tutorial and see how it holds up.

INTRO
What I'm going to show you here is a selection of techniques that should help you with the use of stock images in your icons. Note that this tutorial will focus heavily on what to do and not how to do it, so you might have to consult additional tutorials for help. I particularly recommend the following awesome guides on colour layers, selective colouring and curves. Please also consider that experienced icon makers can probably turn the most horrible idea into something beautiful and vice versa, not to mention that strange effects are often done for humorous purposes, so my good/bad sections are by no means an ultimate list of DOs and DON'Ts, but much rather a selection of things which I think can help to make stock images look better. Alright, I'm all set now, so without further ado let's finally move on to the tutorial!
USE STOCK IMAGES THAT SUPPORT YOUR BASE
not!GOOD EXAMPLE
	Presents are pretty. I love presents and I'm sure you do too. However, did you ever notice how rarely they can be seen floating about in the sky? The random placement of objects, even when coloured and cropped well rarely makes for a usable stock icon.
GOOD EXAMPLE
	Clouds! I think I remember seeing those in the sky before. Well then, let's put that to good use! Think of other situations in which your image supports a certain kind of stock. If you've got an image of somebody sitting at a table, why not add a stock image of a bottle or a glass? Using bases and stock images that go together naturally is one of the best and also the easiest way to improve the appeal of your stock icons.
USE STOCK IMAGES THAT SUPPORT PICTURES IN GENERAL
not!GOOD EXAMPLE
	When eating an apple, have you ever seen a face staring back at you? Maybe you did, but then bad icons are probably the least of your problems. When it comes to that type of stock icon you're better off with reality, unless you're really aiming for the comical effect.
GOOD EXAMPLE
	Now unless you are also averse to garlic and sunlight you should have seen a face staring back at you in the mirror. Or in a picture frame. Or a computer screen. Or several other objects in which faces and/or other images are commonly found and can be placed easily without making too much of a fuss about blending or colour adjustment.
MAKE THE RIGHT ADJUSTMENTS
not!GOOD EXAMPLE
	Alright, that's not too bad for a start. However, it's not too good either, seeing as you can't help but notice the strong contrasts, especially between the green/yellow background and the woman in red. So what do we do?
GOOD EXAMPLE
	We make the right adjustments! This icon's contrast is considerably lower and the differences in colour have been toned down. Stock icons mean you're essentially working with two images. Your base and the stock. For a good icon you need to spot the differences between stock and base and minimise them in a way that allows the two to blend together into a good icon. Play with the colours, brightness and contrast of your two images to reduce differences that make either of the two seem out of place.
ADD STUFF
Wait, what? No, don't worry. I'm not asking you to overload your icon with all sorts of effects now. But I want you to consider that sometimes it can be better to make the stock image a mere part of your icon, not its ultimate focus. Don't add stuff for the sake of adding stuff, but don't forget that stock doesn't automatically rule out the use of other elements, such as brushes, textures or text.
	+		=
	+		=
	+		=
There's no clear line that dictates when an addition is good and when it's too much. Just try different things and see how they work out for your images.
OTHER USES OF STOCK IMAGES
Here are some other things you can do to combine your base with stock images.
	Use them as a border. If you're the type who likes borders then why not try a stock image instead of plain colours? You've got to get the right colour and texture though, otherwise this will probably look out of place. I've used red roses here which go nicely with the colour and general theme of my Utena base.
	Paste them over your base. Here I've got a desaturated straw image on 50% Color Dodge, though this is probably my least favourite use of stock since I find it very difficult to apply in a way that doesn't seem distracting or out of place. You've got to be really careful with the type of stock image you want to use and most of the time lowering its opacity is absolutely necessary.
	Use them like black/white space. Now most of the time this is done with a black or white brush, but textures are sometimes used as well, so why not go for the same idea with a piece of stock? Here I've used a stock images of leafs with a colour similar to the original image, erased parts of it and went from there. Don't use a stock image that's too busy and make sure the colour and contrast matches, otherwise it'll end up looking out of place or drawing attention to the wrong part of the icon.
Those are only some of the things I've seen and/or used myself more frequently, but I'm sure you'll be able to come up with more uses for your stock images. Imagination knows no bounds after all, as long as it doesn't involve talking apples anyway.
CREDITS
All icons shown in this tutorial were made by me and are up for grabs, with or without credit to lunargullicons. I get most of my stock images from this site, the ones used in the tutorial can be found here, here, here, here, here, here, here, here and here. Well, that's it for my first tutorial. It was surprisingly fun to make and I hope that at least some of it was useful to you.