Zoho Social currently doesn't support the usage of cloud storage solutions like Dropbox or Google Drive to post images via the Bulk Scheduler. However, you can use this website to upload and host your images. Once uploaded, click on the image to get a direct link for your Bulk Scheduler spreadsheet. You can then paste the direct link of the image (ending in PNG, JPG, JPEG) to your Bulk Scheduler spreadsheet under the Image URL column.
Also, the .csv or .xls or .xlsx file you upload should include the following information as separate columns:
DATE, CONTENT, LINK URL, IMAGE URL1, IMAGE URL2, IMAGE URL3 and IMAGE URL4