If you have one image in each md file, one handy way to control image size is:
adding css style as follows:
## Who Invented JSON?
`Douglas Crockford`
Douglas Crockford originally specified the JSON format in the early 2000s.

<style type="text/css">
img {
width: 250px;
}
</style>
and the output will be like:
[![enter image description here][1]][1]
If you have more images in each md page, then the handy way to control each image or each customized tag is to define each element in css. For this case for the img tag we could have:
//in css or within style tags:
img[alt="Result1"] {
width: 100px;
}
img[alt="Result2"] {
width: 200px;
}
img[alt="Result3"] {
width: 400px;
}
// try in md one of the methods shown below to insert image in your document:
<br/>
<img src="https://i.stack.imgur.com/xUb54.png" alt="Result1"> <br/>
<img src="https://i.stack.imgur.com/xUb54.png" alt="Result2"> <br/>
<img src="https://i.stack.imgur.com/xUb54.png" alt="Result3"> <br/>
<br/>
in md:<br/>
 <br/>
 <br/>

[1]: https://i.stack.imgur.com/xUb54.png