EDIT: To update new Image Type Column in SharePoint please check this video: https://youtu.be/_ZxBVC9tq9U

Picture column in SharePoint is a readonly column in Power Apps. Here is a workaround how you can update Image/Picture column through Flow/Power Automate using “Send an HTTP request to SharePoint”

Following code might be needed:
Header:
{
“Accept”: “application/json; odata=verbose”,
“IF-MATCH”: “*”,
“X-HTTP-Method”: “MERGE”,
“content-type”: “application/json; odata=verbose”
}

Body:
{
‘__metadata’:{
‘type’: ‘SP.Data.Contractor_x0020_DetailsListItem’
},
‘Photo’:
{
‘__metadata’:{
‘type’:’SP.FieldUrlValue’
},
‘Description’: ‘@{triggerOutputs()?[‘body/FirstName’]}’,
‘Url’: ‘@{items(‘Apply_to_each’)?[‘AbsoluteUri’]}’

},
‘LinkedinURL’:
{
‘__metadata’:{
‘type’:’SP.FieldUrlValue’
},
‘Description’: ‘@{triggerOutputs()?[‘body/FirstName’]}’,
‘Url’: ‘@{triggerOutputs()?[‘body/LinkedinURL’]}’
}
}