View Source ExTDLib.Object.InputThumbnail (ExTDLib v0.0.4)

A thumbnail to be sent along with a file; must be in JPEG or WEBP format for stickers, and less than 200 KB in size.

NameTypeDescription
thumbnailInputFileThumbnail file to send. Sending thumbnails by file_id is currently not supported.
widthnumberThumbnail width, usually shouldn't exceed 320. Use 0 if unknown.
heightnumberThumbnail height, usually shouldn't exceed 320. Use 0 if unknown.

More details on telegram's documentation.