The default HTML Popup for a feature layer displays an HTML table containing the names and values of the layer's attributes. Photos can also be displayed, in addition to alphanumeric content. Instructions provided describe how to add a photo to an HTML Popup tab.
Open ArcMap. Open the attribute table of the target feature class by right-clicking the feature class in the Table of Contents then clicking Open Attribute Table.
Click Options > Add Field. Add a new text field to the feature class's attribute table with a length of at least 50.
Start an editing session in ArcMap. For each feature that will have an image displayed in the HTML Popup, enter the following HTML image tag as a value for the record in the new field: