How do I know how many megapixels have my photo?
Really easy, here's the formula:
(width in pixels x height in pixels) / 1.000.000
For example, an image with a size of 1.200 x 900 pixels has: (1200 x 900) / 1000000 = 1,08 Megapixels
What's the best format and color profile to upload my photos?
What are the high-resolution and "retina" displays?