WPDM - Image Button add-on will help you to replace the text (link label) in download link with a image button. Though, add-on packed with many excellent image buttons already, still there is a option to upload your own button images.
- Install and activate image button add-on.
- Go to admin menu >> Downloads >> Settings >> Buttons Tab
- Select (just click) a button image
- Or upload your own image and select
- Save Changes
That’s all. All of your download link should show with that image.
Admin Option Screenshot: