Try onOne's Genuine Fractals for enlarging fotos. Alien Skin has their Blow Up which does the same thing. I use Genuine Fractals; works great! Of course, the old adage still applies, "garbage in, garbage out". Both companies offer trials so you can see if their software will address your needs.
Several years ago, I began a series of abstract digital photographs. It was later suggested that I download these images to photoshop for future refinement and process. Not particularly familiar with the program, I did so but never set the size of the images. As a result, all of the photographs are low-res and cannot be enlarged to poster size (18? x 24? or 24? x 36?) for an upcoming exhibition.
All the originals were deleted ages ago and I have little recourse but to limit the exhibition to miniatures! Not a very cool situation at all considering most of the abstract imagery would have a greater impact on a larger scale.
*Note: In the late 1990?s, I was working on a television show that employed the use of a Faroudja (company name), Line Doubler. It was an advanced piece of equipment that allowed broadcasters to transmit a Hi-Def image without going to the expense of changing all of their gear. It basically deconstructed the images digitally then reconstructed them for broadcast at a higher resolution. That was over a decade ago!
I am currently looking for a solution to this problem via software or hardware that will allow me to double the resolution of these images.