If you have an Assets field called “article_images”, you can create a simple HTML upload input like so:
<input type="file" name="article_images">
<input type="hidden" name="article_images_filedir" value="1">
The first input is the actual File input, and the second tells Assets which upload directory to place it in.
In time, Assets will also support the
multiple="multiple" attribute on the File input, for uploading multiple files at once, but for that we need a small SafeCracker patch to make it to an official EE release.