Changed
<input src="https://stackoverflow.com/questions/49816990/tick.png" title="Mark as read" type="image" alt="submit" name="mark_read">
to
<button type="submit" name="mark_read" style="padding: 0; border: none;"><img title="Mark as read" src="https://stackoverflow.com/questions/49816990/tick.png" /></button>
Input type failed to submit data because of the image type. works fine now.
1
solved PHP query not updating in db throught form