When using Blockposter for image transfers you must remember to reverse the image if there is any text. And if your prints were made on an inkjet printer, you then would have to photcopy them with a toner printer.
As mentioned earlier, Blockposter is great for simpler images without a lot of detail. When the papers are taped back together, a seam may form at the edges after the transfer is done. See image below. This can be painted in. It is just harder to do on say the sheep or the cow.