What is the rule regarding gelatin? Is all gelatin ok to eat?
No, some gelatins are made of animal derivatives, and if derived from non-kosher animals (or animals that were not slaughtered properly), they must not be consumed.
Because gelatin is extracted from animal bones, its prohibition is not clear cut, and depends on the process of extraction. The Shulchan Aruch (Yoreh De’ah 99) rules that bones of a prohibited animal are kosher, but the Shach quotes the stricter view that the moisture in bones of non-kosher animals is not kosher. Only dry bones are viewed as kosher. According to some authorities, the collagen (gelatin) is part of the natural liquid of the bone, which is therefore prohibited. Moreover, the Shulchan Aruch is referring to the actual bone itself, and not the marrow of the bone, which is treated as meat and is prohibited. If the bone was already cooked with non-kosher meat or bone-marrow, it becomes unkosher. Therefore, one may not eat products with unsupervised animal gelatin.