I had a similar issue the other day using Chingu,  Try naming you image file like this: filename_32x32.png.  Where the 32x32 will be the width and height of the image.  This worked for me.

This is a new book, currently in beta, written by Mark Sobkowicz through The Pragmatic Bookshelf (https://pragprog.com/book/msgpkids/learn-game-programming-with-ruby).  I went ahead and bought it and am loving it.  The book asumes that you understand Ruby to some extent, at least the basics of building arrays, classes, and methods.  This book has helped me see the setup and goes into detail with why things are how they are.  Very good intro book for someone looking to get started with Gosu.  You will build 5 games by the end of the book and the author gives suggestions at the end of the chapters for you own personal additions to the game.

Ross

I recently started using Gosu and Chingu, and have had a blast playing with the libraries.  My question is that since Chingu isn't being updated anymore is it still viable to use and if not is there anything else that is compariable.  I have seen some options here on the forums that look good like miniGL but I didn't see any documentation to get started with it.  Anyway, thanks for any comments.