Dear candidate, the signature should be white background with black pen signature which must not be in capital letters. 2.5 x 3.5 inches with 72 DPI is the dimension required for signature. Left-hand thumb impression should be file size: 10 kb-50 kb in JPG/JPEG format. (If due to some reason the left-hand signature can’t take place then do with the right hand). For more information, you can check:

https://medicine.careers360.com/articles/neet-photo-size-format-documents

Hope, it helps!