I'm sorry to hear about the difficulties you've had with the distorted image in the document preview. I presume you're reporting this for a Jive-x external environment. If this is incorrect, please let me know.
If the spreadsheet is converting with distortion, I would recommend first trying to isolate the cause. You might re-create the same spreadsheet without the image and also create a separate spreadsheet with just the image to see which exhibits this behavior. Once you've identified if the issue is specifically around the spreadsheet or the image, you may want to try using a different format to see if the document preview converts properly. So for example, if your spreadsheet is a Microsoft Excel .xlsx file, try converting it to an .xls (legacy) file. If the image is a PNG file, try converting it to a JPEG file. Once you've identified a feasible workaround, you're welcomed to apply this moving forward for similar issues.
If you need more direct troubleshooting assistance or need to report a potential conversion bug, I would encourage submitting a support case in your secret Jive Customer group. Please provide a sample file, if available, for analysis and testing. If you're not familiar with the case submission process, please reach out to your community manager for guidance.
Let me know if you have any other questions with this.