Scroll Up plugin lightweight plugin that creates a customizable "Scroll to top" feature in any post/page of your WordPress website.
Oh, and great support too!
This plug in works quite well. Only you need to change some of the CSS to achieve a look which ties in with your page design (colour, size, etc.). Best to overwrite it in your child theme!
BTW: instead of using an image I simply inserted the HTML font symbol code for an "up arrow" (↑ or ⇧) and styled the font accordingly. You can find the codes here: http://character-code.com/arrows-html-codes.php
Only reason no 5 star is there are no instructions to customize. Would love to change the font, color, etc to match my theme but there are no instructions included to do so.