I've tried...
1. Making the image exactly 140 x 200.
2. Making the image smaller than 140 x 200.
3. Uploading directly to Lemmasoft.
4. Using a URL after uploading to another website.
5. Saving as a PNG
6. Saving as a JPG.
I'm honestly not certain what else to do. D:
Other avatars on the forum don't appear to have this issue, so I'm quite confused.
EDIT: Upon taking a second look, perhaps other avatars DO have this issue. If that's the case, it's most likely due to the forum software (i.e. nothing anyone here could fix/offer a workaround for).