Telemedicine systems are used to transfer medical images between hospitals and doctors for consultation in many countries recently. It is crucial to ensure integrity of medical images transferred on unencrypted channels. Many medical image watermarking techniques have been proposed in the literature to deal with this problem. Thermal imaging to detect dense vascular regions is a new medical imaging modality gaining popularity to enhance diagnosis of breast cancer. Thermal images with large smooth areas and Region of Interest (ROI) have different characteristics compared to traditional medical images and require new image watermarking methods. A new thermal image watermarking algorithm utilizing Integer Wavelet Transform (IWT), Modified Difference Expansion (MDE) and Shamir's Secret Sharing Scheme (SSSS) has been proposed for e-healthcare applications in this paper. IWT coefficients of thermal image are expanded by the MDE to make more consecutive blocks expandable. Location Map (LM) becomes more compressible if there are many consecutive blocks. Thus, larger ROI can be watermarked by the proposed method. The method also uses SSSS to share LM into meaningless shares embedded into border regions. Sharing LM by the SSSS makes it possible to reconstruct it even if some of the thermal image borders are removed inadvertently or modified on purpose to break the watermark. Experimental results indicate that the proposed method has better embedding capacity and good imperceptibility compared to similar methods reported in the literature. Besides, it has expanded ROI size and also is the first method which considers border region attacks in medical image watermarking.