href image link download on click

<a download="custom-filename.jpg" href="/path/to/image" title="ImageName">
    <img alt="ImageName" src="/path/to/image">
</a>

It's not yet fully supported caniuse, but you can use with modernizr (under Non-core detects) to check the support of the browser.

The easiest way of creating download link for image or html is setting download attribute, but this solution works in modern browsers only.

<a href="/path/to/image" download="myimage"><img src="/path/to/image" /></a>

"myimage" is a name of file to download. Extension will be added automatically Example here