While most graphic files on the internet have a resolution of 72pixel/inch, you need to keep in mind that this resolution is often not suitable for printing. To illustrate that, let's take two images that have the same number of pixels (348 x 350):
One is set at 72pixels/inch:
And the other one is set at 144pixels/inch:
As you can see here, there's no way to tell the difference between them on the screen because your browser displays these images according to their sizes in pixels, regardless of their resolution.
Now if you write a LaTeX document that includes them both:
Here's what you get as the resulting pdf:
As you can see, the original 72px/in image will appear 'too big', pixelized and blurry on your piece of paper, whereas the 144px/in one will be twice as small and keep its sharpness.
So don't hesitate to experiment with resolution when making LaTeX based documents.
That's all for today!