How do you check the DPI of an image?

I'm curious to know, could you please elaborate on the process of checking the DPI, or dots per inch, of an image? Is there a specific software or tool that you recommend for this task? Additionally, would the method differ depending on the type of image file, such as JPEG, PNG, or TIFF? I'm interested in understanding the steps involved and any potential considerations I should keep in mind when performing this check.