If you work with pictures and images, there are three main related features: picture size, resolution, and dimension. The size is something related to megabytes. The resolution and dimension are related to pixels, which are the cells of a pictures. Sometimes you may need to change the dimensions or size of an image for a particular environment, so you need to understand the concepts of Dots Per Inch (DPI) or Pixels per Inch (PPI).
A pixel is the smallest unit that constructs a digital image or graphic, on a video display system. The word pixel comes from the abbreviations of picture and element. Computer or TV screens display pictures by dividing the screen into millions of pixels sequenced in rows and columns. Each pixel consists of a number of bits that determines the color. The number of pixels defines the quality of your image. The more pixels per inch your image has, the better your image is (and the higher its resolution is as well). Fewer pixels per inch means lower quality image and lower resolution. Pixels also play the role of a standard unit for measurement for images, as well as for all kinds of screens. Usually, there are certain requirements as to the dimensions and resolution mentioned by websites or online platforms.
The term DPI (dots per inch) is linked with the resolution of an image. It is an arithmetic term that shows how many dots per linear inch the image has. Usually, screens have some standards for resolution. To successfully do pixel conversions, e.g. convert pixels to millimeters or inches, we need to know the dimensions of the image and its resolution.