Choose the representation that matches the data
Base64 encodes bytes as text for transport; it is not encryption and it does not make an object private. Provide the encoded payload exactly as expected by the upload tool. Avoid adding a data-URL prefix unless the tool documentation explicitly asks for one, and do not encode an already encoded string a second time.
For binary files, preserve the original bytes during encoding and verify the resulting object by downloading it and comparing its type or checksum where available. A corrupted or truncated Base64 value can still look like text while producing an unusable file. Keep large payload limits and request-size constraints in mind.
Set metadata and access deliberately
The content type describes how the object should be interpreted, for example as an image or PDF. A wrong type can affect browser previews or downstream consumers even when the stored bytes are correct. Use the format's standard media type and verify the object after upload.
Encoding does not change who can read the object. Apply the intended bucket or object access policy, avoid putting secrets into publicly accessible storage, and choose a clear key that does not expose personal information. If an upload fails, check both the encoded payload size and the destination permissions.