How can I attach a view for each row of another view?
1) Viewfield is a good solution.

Views attachment attach to a views display (Page, Block etc) not to each row.

So, first remove the Contextual filter uid.

Then add one more field, the flag of the node. Then you will have User_Name, Node Image, Flag and each row will represent a node.

2) Another option is to use the Views_Merge_Rows. In the Merge Rows settings you have to set the Merge Options for the User Name field as "Use the values of this field as filter" and uncheck the "Exclude this field from display". For the other fields select the "Use the first value of this field".

3) If you don't want to use a contributed module use the "Group results together" on the Format display settings. Group by user name and then Exclude from display the User Name field.