There have been a few posts highlighting a nice 3d relief portrait of some bears in a forest.
For those who couldn't attend the 2015 McGrew's Camp, Michael Mezalick discussed this model in one of his presentations. He noted that if someone wanted to scale the model to 3/4-inch thickness for machining in MDF, then there are some really thin spots which could easily be damaged while handling (or even during cutting). He then proceeded to show a method of thickening the inner portion of the portrait (not the frame) by using a technique similar to the one demonstrated in the Creating a Dished Recess tutorial in which a Multiply combine model is used to raise the edges more than the center portion. As he stated, one disadvantage of this method was that some detail was lost around the edges of the portrait.
After the camp I decided I'd like to try one of these large 3d portraits, so I found the model on ebay (just search for "cnc 3d relief stl bears" and you should find it) and purchased it. Turns out I bought it on a Russian holiday, because it took a couple of days to receive the download link for it! After playing around with it a bit, I also wanted to thicken it somewhat, but I used a tilt to accomplish the effect.
When I imported the model into Aspire, I scaled its original thickness to 0.75 inch, which resulted in a portrait size of 17.5 X 24.7. The low spot of the model is the flat region in the top middle, and the remaining thickness is only about 0.060". Notice how much of the interior frame is visible at the top of the portrait.
To modify only the interior of the portrait, I created a rectangle vectors around the interior of the frame and obtained separate frame and image components by using Split Component tool. Once I had the bear image separated from the frame, I just used the Tilt command to raise the top edge, which gave me a thickness in the problem area of approximately 1/4 inch. Notice how there is less interior frame visible at the top in this image, but the bottom isn't really different.
Anyway, this is another method of accomplishing the same goal, but it doesn't lose any edge detail. Apologies to Michael if I misrepresented his presentation. I found the presentation very informative, and it inspired me to try this myself! Now all I have to do is set aside a whole weekend to cut this!