To use a sequence of image files to create an animation, the file name must be expressed in one of the following three formats:
name.#.ext
name.ext.#
name.#
where name is the base name of the file; # is the frame number (with or without leading 0s), ext is the file extension of the file.
To use a sequence of image files to create an animated file texture, the file extensions must be separated from the basename and/or the extension by dots (.).
For example, the following works:
test.1.iff
test.0001.iff
test.1
test.0001
test.iff.1
test.iff.0001
But the following would not work:
test1
test0001
test1.iff
test0001.iff