Due to a difference in Safari's copy-paste implementation from other browsers, Textbox.io does not support direct-pasting of images from applications such as Preview and Adobe Photoshop.
Use a different browser
Direct paste of images from other browsers (such as Google Chrome) is supported.
Save and Upload the Image
Saving images to your local filesystem and manually uploading them is a way to get them into the editor.
(Pasting from Microsoft® Word only) Select the image as part of the document
Textbox.io handles Microsoft Word document (.doc, .docx) content slightly differently than image content. It is therefore possible to select the image as part of a document. To do this, select the image such that it is highlighted as part of the document.