Because of the limit to how many images you can see in your account on imgur, I use imgur for picture box games and
www.slickpic.com for slideshow quizzes.
You get 1,000 images on the free account and the interface is relatively simple. You can create folders as well which is handy when organising. The best feature though is that the URLs aren't random letters and numbers which means you can copy most of it and then quickly add in the name of the file. All the names of my files are numbers so you can't see the answer in the image source link which makes it even easier to create all of the links for each slide really quickly (especially if you're importing from Excel).
For the box office series that I'm doing at the moment, I have most of the URLs entered into the quizzes but don't have all the images yet. All I need to do is upload the images in the correct album and give it the corresponding number and it then works in the quiz.