You may have noticed that your question got moved to "client-side technologies". That is because what you want to do is limited by the user's browser and operating system. If I understand your first question correctly, the user controls whether an input box will "auto-complete" through browser settings.
I'm not sure in your second question whether you intend to style a combo box with images, or if you simply want to populate a combo box with image file names as values. The former is impossible because combo boxes are not styled by the browser. The look of a combo box is determined by your operating system. There are very few things you can change about them. As an alternative, you can check into Flash or Google "html drop-down styling" (note: drop-downs are not the same as form-based combo boxes).
If it is the latter, then you have some 'splaining to do. Are the files listed in a database? Are you just trying to get filenames out of a folder and list them in a combo box? Do you want an image to appear immediately elsewhere in your page? (That requires Javascript, by the way...)
