As I pointed out, but you seem to have overlooked, you don't have to leave the dpi setting at whatever Anim8or (or other image producer) uses. You can change the dpi settings of any image without changing anything else about that image.
For example, you can take an image consisting of 2100 x 3070 pixels, one intended for a 7x10" image at 300 dpi but which has internal values of 72x72 dpi, and change its dpi values of 72x72 to be 300x300, leaving the image file otherwise unchanged.
Irfanview and Gimp are two of the programs with graphical GUIs which include that capability. ImageMagick can change dpi settings, too, if you prefer a command-line utility. ( convert -units PixelsPerInch input.png -density 300 output.png ) I'm sure there are others.
I agree that it would be nice if the dpi settings could be specified to Anim8or before it writes the image to a file, but it isn't essential if you're willing to add the dpi modification to your workflow.