Card attachments are files uploaded to cards. Attachments appear in the "Attachments" section of the card detail. You can add attachments from:
- Your Computer
- Google Drive
- Any Link
NOTE: Attachments from your computer create an actual copy within Trello. Attachments from Google Drive, Dropbox, Box and OneDrive simply link back to the document in its respective location. Documents that are attached with Google Drive and OneDrive can be edited and saved in their respective applications and do not need to be downloaded, saved, and reattached to your card.
Click the front of the card to open it. Click the "Attach File" button on the right side of the card to upload. On newer versions of Chrome and Safari, you can simply drag and drop the file from your desktop on to the card.
If you attach an image file to a card, Trello will automatically create a picture to put on the front of the card and in the header of the card back. These are called "card covers." You can click a card to open it to choose which image to use as a card cover (or to remove the card cover if you wish).
Card covers can be disabled on a board by a board admin. To turn them off, open the board's Additional Settings in the boards Menu and uncheck "Card Cover Images Enabled".
Bonus Tip: Animated gifs that are less than 300 pixels wide will display as animations on card covers.
You can preview your attachments within Trello without having to download them by clicking on the thumbnail of the attachment from the card back to open the preview. This allows you to quickly view documents, images, .PDFs, and almost anything you have attached to your card.
There is a 10 MB file upload limit per attachment, however Business Class and Trello Gold members have a 250 MB file upload limit per attachment. It's not possible to upload attachments via the mobile site. There is no limit on the number of attachments you can have on a card or board. Neither is there an account data storage limit.
The 10MB file upload only applies to files uploaded from your computer. It does not apply to files attached from Google Drive, Dropbox, Box or OneDrive.
If you attach a file from your computer (using the "Computer" option in the "Attach File" menu), the attachment is stored in Amazon S3. The URLs for the attachments are cryptographically unguessable, meaning that no one is going to be able to guess your attachment URL. However, if you share the URL for a Trello attachment, anyone with the URL will be able to see the attachment. Deleting the attachment in Trello removes the file from Amazon S3.
If you need extra security, we recommend using Google Drive for attachments. You can attach files from Google Drive directly to Trello and specify fine-grained access to the file via the Google Drive interface.