Board Thread:Support Requests - Designing Your Wiki/@comment-33391139-20180519051005/@comment-24142930-20180519185334

Try adding this code to your personal javascript, replacing the URL with the full image URL of your choice.

window.pPreview.noimage = 'https://vignette.wikia.nocookie.net/borderlands/images/f/f5/%D0%97%D0%B0%D0%B3%D0%BB%D1%83%D1%88%D0%BA%D0%B0.png/revision/latest/scale-to-width-down/200?cb=20160122074659&path-prefix=ru';

Test in your personal JavaScript page first ( on your wiki), if it works, add the code to. It can take several hours for a member of staff to review and approve the JavaScript code though.

Edit: Just to clarify, you don't have to add it to  if you only want to have the change applied for you personally.