From what I can find, the best way to tell the difference between I. indica and I purpurea is in the sepals. Based on your photo I am incline to agree with Janet, but it is difficult for me to say for sure without a closer shot.
Ipomoea purpurea should have short more acute sepals like the ones shown in this link.
Ipomoea indica should have longer, tapered sepals like the ones in this photo from my yard.
