how to create a "save file as" prompt ?

i have some hi-resolution images and i would like to create a text link that
prompts a "save file as" pop up window to appear, so that users can download
the images without having to open the files first. how can i do this?

easiest and most reliable- give instructions to Right-click and choose
"save link" to their hard drive And the other variations for various
browsers (and to note WHERE and with WHAT filename they are saving it, if
it's klutzy type of audience) .

other choices, making the .zip files which will force a download for almost
everyone, but then you have to deal with the people having a ZIP utility.

or altering the mime type on the server so that it will force the actual
unaltered files to download in ~most~ browsers.

i have some hi-resolution images and i would like to create a text link that
prompts a "save file as" pop up window to appear, so that users can download
the images without having to open the files first. how can i do this?