LMS uploads fail for reasons that have nothing to do with the file being too big in the abstract. Canvas caps a submission at 5 GB in its standard guide but states 500 MB in the Assignment Enhancements guide, and its file picker allows exactly one file at a time. Blackboard's real ceiling is whatever an administrator configured, with a 300MB per-file limit in the student guide and a 25MB processing limit inside SafeAssign. Moodle does not have a limit at all in the abstract — it has a cascade: server LimitRequestBody, then PHP post_max_size and upload_max_filesize, then a site-wide maximum, then course settings, then the assignment itself, and the smaller one always wins. Brightspace accepts up to 2GB per file but uploads in 10MB chunks with a two-minute timeout per chunk, so a large file on weak campus wifi dies halfway and the error says nothing useful. Different platforms, one shared failure: a phone photo or a scanned worksheet at full weight hitting a limit nobody documented in one place. What works is compressing before you pick the file, so the upload is a single small transfer rather than a retry loop at 11:58pm. Skwish resizes, converts format and compresses entirely in the browser with a per-file before and after readout, and packs a whole set into one ZIP — no account, no server upload.