diff --git a/app.js b/app.js
index 677d3fa..dbbecc9 100644
--- a/app.js
+++ b/app.js
@@ -22,6 +22,9 @@ var i18n = require('i18n')
 var flash = require('connect-flash')
 var validator = require('validator')
 
+// utils
+var getImageMimeType = require('./lib/utils.js').getImageMimeType
+
 // core
 var config = require('./lib/config.js')
 var logger = require('./lib/logger.js')
@@ -548,6 +551,9 @@ app.post('/uploadimage', function (req, res) {
                 Body: buffer
               }
 
+              var mimeType = getImageMimeType(files.image.path)
+              if (mimeType) { params.ContentType = mimeType }
+
               s3.putObject(params, function (err, data) {
                 if (err) {
                   logger.error(err)
diff --git a/app.json b/app.json
index 0ed11d7..e09d4c0 100644
--- a/app.json
+++ b/app.json
@@ -10,9 +10,6 @@
     "repository": "https://github.com/hackmdio/hackmd",
     "logo": "https://github.com/hackmdio/hackmd/raw/master/public/hackmd-icon-1024.png",
     "success_url": "/",
-    "scripts": {
-        "postdeploy": "./node_modules/.bin/sequelize db:migrate"
-    },
     "env": {
         "BUILD_ASSETS": {
             "description": "Our build script variable",
diff --git a/bin/heroku b/bin/heroku
index 1228b28..2472734 100755
--- a/bin/heroku
+++ b/bin/heroku
@@ -3,8 +3,6 @@
 set -e
 
 if [ "$BUILD_ASSETS" = true ]; then
-  BUILD_ASSETS=false npm install
-
   # setup config files
   cat << EOF > .sequelizerc
 var path = require('path');
diff --git a/lib/utils.js b/lib/utils.js
index 6c36549..d9289dc 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -3,3 +3,23 @@
 exports.isSQLite = function isSQLite (sequelize) {
   return sequelize.options.dialect === 'sqlite'
 }
+
+exports.getImageMimeType = function getImageMimeType (imagePath) {
+  var fileExtension = /[^.]+$/.exec(imagePath)
+
+  switch (fileExtension[0]) {
+    case 'bmp':
+      return 'image/bmp'
+    case 'gif':
+      return 'image/gif'
+    case 'jpg':
+    case 'jpeg':
+      return 'image/jpeg'
+    case 'png':
+      return 'image/png'
+    case 'tiff':
+      return 'image/tiff'
+    default:
+      return undefined
+  }
+}