Multipart Uploads only handles files larger than 10 MB. We set the limit because uploading files smaller than 10 MB in multipart mode does not provide any significant performance improvement over Direct Uploads.
By default, Uploadcare won't treat files larger than 100 MB as images regardless of the upload method. However, this limit can be adjusted on a per-project basis upon request.
Multipart Uploads for images will also work with Uploadcare Widget since it's an Upload API client. Keep in mind the threshold after which files get uploaded in the multipart mode is controlled via the Multipart Minimum Size option which defaults to 25 MB.
Have fun with larger images and drop us a line in case you have any questions.