Loading 300dpi images for download

Question

How can I add 4x5 300 dpi images to my website for download from clients without the images being enlarged on the website?

Answer 1

...without the images being enlarged

To me this implies that you do actually want to display these images, which the user wants to download anyway, but at normal size? With these being huge images they will naturally take a while to display, but you can just set a width on the img element and the browser will adjust the height to the appropriate aspect ratio. The user then uses the context menu to save the image; just like any other image.

<img src="massive-300dpi-image.jpg" width="500" alt="Big Image">

However, if you do want to provide a download-only solution then see @Su' link in the comments.