Hello,

If I am getting right what you are after, you will need to develop a custom form control that will upload the file to media library and use it in your custom document type: Developing form controls.

In terms of your second question, could you please describe what you mean by your custom images? If you want to allow only some files extensions you can specify Media file allowed extensions (Site manager -> Settings -> Content -> Media).

Best regards,
Michal Legen