Why does image use display: inline but behaves like an inline-block element

Question

Why is the default display style for image inline instead of inline-block?

Is there any difference between inline and inline-block for img elements, from what I can

Answer 1

The first part of your question is already answered, so I shall not repeat.

For the second part, some browsers like Firefox renders a no-image img tag as a span even when width and height attributes are specified in CSS.

You can try it out yourself with this HTML code:

And corresponding CSS:

img {
    height: 100px;
    width: 100px;
    background: cyan;
}
#iblock {
    display: inline-block;
}

Or see the difference in rendering effect with this Demo on JsFiddle.