It is easy! Upload your image in JPG or PNG format and The Rasterbator will let you customize your settings. Choose how many pages wide you would like the final image to print, the size of paper and orientation and Posterizer will create a PDF or JPG images you can download and then print the pages off on your home printer.
There are lots of options including the ability to have effects and other options. Depending on how you want your final poster to look you can spend a great deal of time tweaking settings. It was also nice there was no cropping of the image when it was printed across multiple pages. Overall a very nice option for printing posters.
The Not So Good
Sometimes to many options are a bad thing. Hard to know what to select on occasion. Thankfully you can play with it and see the preview as you go. For really large posters there is a limit of 1000 pages. If you want or need to print posters larger than that you need to get the standalone version of the software.
The Rasterbator is probably your best option for printing posters and larger images across multiple pages. It is free but the author does request donations. Considering how many options and features the service has it would be nice if the author is compensated for their work. Please consider a donation if you use the service.