
Did you know that the natural path the eye does when scanning is from left to right, up to down? I learned that from my advertising class back in school. People tend to start from the left to right, up to down of a page in a given instant.
Dependent on how the image found fit the page, really. Some images are better of being on the top-center just below the title of the page. Others are best suited to simply provide a thumbnail aligned to the left or right of the 1st paragraph.
It's pretty simple. Do not post images of cars when you are talking about food.
Now how about the dimensions of your image of choice? It really depends.
Most blogs normally run around your page taking up around 800px in width or more. Have the image around 200-300px in width with its respective height. This way, your image won't flood the whole article. If your image is way bigger than this, then try resizing or atleast linking your image to its original file. It's like creating a thumbnail to click.
When resizing, be sure to keep proportion. Unproportional images are truly unattractive aren't they?
You have a lot of images you'd like to use! 20images for an article 2paragraphs long! Now that's going to be a bit troublesome. If you can, try narrowing down your choice of images. Posting too many images within the article could ruin the whole layout and make the impression that you're a noob blogger who finally discovered the way to post images online, which isn't really nice.
If you can't help but keep all those images, choose the best and include these images in your article. As for the rest, try making smaller sized thumbnails like 50x50px ones and post them at the very end of your article.
Remember that when you put images on your page, they will add to the time your page can fully load. This is where having those photo-hosting sites become useful.
By the time you get the idea of what image to use, you'll be in that predicament wherein you'll realize that you don't own such an image.
Photos original taken are best to use as these could reflect more what you are trying to say. It has your personal touch.
Nevertheless, there are those free stock photos that you can find online. Just sign up and download them.