diff --git a/web/media/media-utils.js b/web/media/media-utils.js
index f1df17903..d7be56b3f 100644
--- a/web/media/media-utils.js
+++ b/web/media/media-utils.js
@@ -1,274 +1,274 @@
 // @flow
 
 import { detect as detectBrowser } from 'detect-browser';
 import * as React from 'react';
 import { thumbHashToDataURL } from 'thumbhash';
 
 import { fetchableMediaURI } from 'lib/media/media-utils.js';
 import type {
   MediaType,
   Dimensions,
   MediaMissionStep,
   MediaMissionFailure,
 } from 'lib/types/media-types.js';
 import { getMessageForException } from 'lib/utils/errors.js';
 
 import { probeFile } from './blob-utils.js';
 import { decryptThumbhashToDataURL } from './encryption-utils.js';
 import { getOrientation } from './image-utils.js';
 import { base64DecodeBuffer } from '../utils/base64-utils.js';
 
 async function preloadImage(uri: string): Promise<{
   steps: $ReadOnlyArray<MediaMissionStep>,
   result: ?Image,
 }> {
   let image, exceptionMessage;
   const start = Date.now();
   const imageURI = fetchableMediaURI(uri);
   try {
-    image = await new Promise((resolve, reject) => {
+    image = await new Promise<Image>((resolve, reject) => {
       const img = new Image();
       img.src = imageURI;
       img.onload = () => {
         resolve(img);
       };
       img.onerror = e => {
         reject(e);
       };
     });
   } catch (e) {
     exceptionMessage = getMessageForException(e);
   }
   const dimensions = image
     ? { height: image.height, width: image.width }
     : null;
   const step = {
     step: 'preload_image',
     success: !!image,
     exceptionMessage,
     time: Date.now() - start,
     uri: imageURI,
     dimensions,
   };
   return { steps: [step], result: image };
 }
 
 /**
  * Preloads a media resource (image or video) from a URI. This sends a HTTP GET
  * request to the URI to let the browser download it and cache it,
  * so further requests will be loaded from the cache.
  *
  * For raw images, use {@link preloadImage} instead.
  *
  * @param uri The URI of the media resource.
  * @returns Steps and the result of the preload. The preload is successful
  * if the HTTP response is OK (20x).
  */
 async function preloadMediaResource(uri: string): Promise<{
   steps: $ReadOnlyArray<MediaMissionStep>,
   result: { +success: boolean },
 }> {
   const start = Date.now();
   const mediaURI = fetchableMediaURI(uri);
   let success, exceptionMessage;
   try {
     const response = await fetch(mediaURI);
     // we need to read the blob to make sure the browser caches it
     await response.blob();
     success = response.ok;
   } catch (e) {
     success = false;
     exceptionMessage = getMessageForException(e);
   }
 
   const step = {
     step: 'preload_resource',
     success,
     exceptionMessage,
     time: Date.now() - start,
     uri: mediaURI,
   };
 
   return { steps: [step], result: { success } };
 }
 
 type ProcessFileSuccess = {
   success: true,
   uri: string,
   dimensions: ?Dimensions,
 };
 
 const browser = detectBrowser();
 const exifRotate =
   !browser || (browser.name !== 'safari' && browser.name !== 'chrome');
 
 async function processFile(file: File): Promise<{
   steps: $ReadOnlyArray<MediaMissionStep>,
   result: MediaMissionFailure | ProcessFileSuccess,
 }> {
   const initialURI = URL.createObjectURL(file);
   if (!exifRotate) {
     const { steps, result } = await preloadImage(initialURI);
     let dimensions;
     if (result) {
       const { width, height } = result;
       dimensions = { width, height };
     }
     return { steps, result: { success: true, uri: initialURI, dimensions } };
   }
 
   const [preloadResponse, orientationStep] = await Promise.all([
     preloadImage(initialURI),
     getOrientation(file),
   ]);
   const { steps: preloadSteps, result: image } = preloadResponse;
 
   const steps: MediaMissionStep[] = [...preloadSteps, orientationStep];
 
   if (!image) {
     return {
       steps,
       result: { success: true, uri: initialURI, dimensions: undefined },
     };
   }
 
   if (!orientationStep.success) {
     return { steps, result: { success: false, reason: 'exif_fetch_failed' } };
   }
   const { orientation } = orientationStep;
 
   const dimensions =
     !!orientation && orientation > 4
       ? { width: image.height, height: image.width }
       : { width: image.width, height: image.height };
   if (!orientation || orientation === 1) {
     return { steps, result: { success: true, uri: initialURI, dimensions } };
   }
 
   let reorientedBlob, reorientExceptionMessage;
   const reorientStart = Date.now();
   try {
     const canvas = document.createElement('canvas');
     const context = canvas.getContext('2d');
     canvas.height = dimensions.height;
     canvas.width = dimensions.width;
 
     if (orientation === 2) {
       context.transform(-1, 0, 0, 1, dimensions.width, 0);
     } else if (orientation === 3) {
       context.transform(-1, 0, 0, -1, dimensions.width, dimensions.height);
     } else if (orientation === 4) {
       context.transform(1, 0, 0, -1, 0, dimensions.height);
     } else if (orientation === 5) {
       context.transform(0, 1, 1, 0, 0, 0);
     } else if (orientation === 6) {
       context.transform(0, 1, -1, 0, dimensions.width, 0);
     } else if (orientation === 7) {
       context.transform(0, -1, -1, 0, dimensions.width, dimensions.height);
     } else if (orientation === 8) {
       context.transform(0, -1, 1, 0, 0, dimensions.height);
     } else {
       context.transform(1, 0, 0, 1, 0, 0);
     }
 
     context.drawImage(image, 0, 0);
-    reorientedBlob = await new Promise(resolve =>
+    reorientedBlob = await new Promise<Blob>(resolve =>
       canvas.toBlob(blobResult => resolve(blobResult)),
     );
   } catch (e) {
     reorientExceptionMessage = getMessageForException(e);
   }
   URL.revokeObjectURL(initialURI);
   const uri = reorientedBlob && URL.createObjectURL(reorientedBlob);
   steps.push({
     step: 'reorient_image',
     success: !!reorientedBlob,
     exceptionMessage: reorientExceptionMessage,
     time: Date.now() - reorientStart,
     uri,
   });
 
   if (!uri) {
     return {
       steps,
       result: { success: false, reason: 'reorient_image_failed' },
     };
   }
   return { steps, result: { success: true, uri, dimensions } };
 }
 
 type FileValidationSuccess = {
   success: true,
   file: File,
   mediaType: MediaType,
   uri: string,
   dimensions: ?Dimensions,
 };
 async function validateFile(file: File): Promise<{
   steps: $ReadOnlyArray<MediaMissionStep>,
   result: MediaMissionFailure | FileValidationSuccess,
 }> {
   const [probeResponse, processResponse] = await Promise.all([
     probeFile(file),
     processFile(file),
   ]);
   const { steps: probeSteps, result: probeResult } = probeResponse;
   const { steps: processSteps, result: processResult } = processResponse;
 
   const steps = [...probeSteps, ...processSteps];
 
   if (!probeResult.success) {
     return { steps, result: probeResult };
   }
   const { file: fixedFile, mediaType } = probeResult;
 
   if (!processResult.success) {
     return { steps, result: processResult };
   }
   const { dimensions, uri } = processResult;
 
   return {
     steps,
     result: {
       success: true,
       file: fixedFile,
       mediaType,
       uri,
       dimensions,
     },
   };
 }
 
 function usePlaceholder(thumbHash: ?string, encryptionKey: ?string): ?string {
   const [placeholder, setPlaceholder] = React.useState<?string>(null);
 
   React.useEffect(() => {
     if (!thumbHash) {
       setPlaceholder(null);
       return;
     }
 
     if (!encryptionKey) {
       const binaryThumbHash = base64DecodeBuffer(thumbHash);
       const placeholderImage = thumbHashToDataURL(binaryThumbHash);
       setPlaceholder(placeholderImage);
       return;
     }
 
     (async () => {
       try {
         const decryptedThumbHash = await decryptThumbhashToDataURL(
           thumbHash,
           encryptionKey,
         );
         setPlaceholder(decryptedThumbHash);
       } catch {
         setPlaceholder(null);
       }
     })();
   }, [thumbHash, encryptionKey]);
 
   return placeholder;
 }
 
 export { preloadImage, preloadMediaResource, validateFile, usePlaceholder };