The first step is to identify what you intend on 3D printing. By that I mean, will the objects be predominantly mechanical-like with curvilinear surfaces or will they be organic? If the former, stay with CAD. If the latter, look into digital sculpting.

The hoof prints clearly fall strongly into objects that digital sculpting will easily take care of.

Can it be done in traditional CAD? Partially, but mostly with poor results. Importing a 2D image to generate a heightfield model/mesh. This will be the laziest approach and will also look like garbage. Can the generated mesh resolution be cranked up? Yes, but most CAD software don't do well with high-polygon meshes beyond basic scaling.

Can organic-modeling plug-ins like T-Splines and Clayoo be used to 3D model the prints? Up to a point. Modeling a human head is do-able in the realm of CAD as demonstrated in this thread:
http://www.tsplines.com/forum/viewto...t=30286#p44419
However, any attempts to add super-fine detail (textured eyebrows, lashes, creases, wrinkles) will have the same results as trying to perform surgery with a butterknife.

Digital sculpting programs like Pixologic's ZBrush and Autodesk's Mudbox are geared to make organic things. An intermediate-level user should be capable of cranking out a couple dozen different hoof models in the course of an afternoon.

The ZBrush workflow would look something like.... Starting from a 2D picture of the foot/hoof print, it can be immediately applied as a mask on a puck. There are at least a dozen applicable tools that'll sculpt the unmasked regions to the desired depth to create the shape of the paw-pad. Next, either using more detailed reference images or pulling from the existing library of Alpha-masks, insane texture detail can be further added to the imprints. (Whether the 3D printer can replicate ultra-fine detail is another department) Here's a YouTube example of using an Alpha-Mask to imprint texture detail onto a sculpt:



If there's any doubt about digital sculpting's suitability for organic models, just look at the gallery threads: http://www.zbrushcentral.com/zbcinfinite.php and search the posts where they've 3D printed their models like this one:
http://www.zbrushcentral.com/showthr...lry-Sketchbook

As for the geometric designs, I've seen plenty of similar examples done by sculptors: