I am not quite sure how I stumbled on this great resource, but nevertheless, I am sharing it with you. (If you're Southern, that's y'all, or the plural, all y'all.) A while ago, I showed you the Rasterbator, which converts digital pictures into huge newspaper-style half-tone photos. Now, I have found Block Posters, which converts a digital picture into a multi-sheet PDF like a huge advertising poster. This is not exactly the picture I would have chosen for my example, but I lifted it from their site.
Like Rasterbator, you can select the size you want the output print to be, they instantly convert it to a PDF and you just print it off on your printer. I do warn you that this will be a complete and total ink hog, especially if you do a large piece. The smaller the image, the more pixellated the image will be, but you can upload images up to 1mb in size. Here are some examples of posters on their gallery.
The image above was printed, flipped, reprinted, and put on a corner wall. People suggest either adhering the image to foam core or directly onto the wall using spray adhesive. I just tried Block Poster with this picture I took of a gardenia and then scaled it to five portrait pages across and three down. I am not sure whether I will print it out, but it looks good in the PDF.