$file = Export["tmp/img.png", Plot[Sin[x], {x, 0, 2 Pi}], "PNG"];
$req = HTTPRequest[URL["https://api.imgur.com/3/image"],
<|Method -> "Post",
"Headers" -> {
"Authorization" -> "Client-ID 93d5e807261cc90",
"Accept" -> "application/json"
},
"Body" -> {"image" -> File[$file], "type" -> "file"}
|>
]
URLRead[$req]