Step 1: Create a sample data entity as shown below. It uses EcoResProductImage table which holds the image container of the items.
Step 2: Check the odata feed in the browser. You can see the Base64 images are exposed in “MediumSize” field as shown below.
Step 3: Create a sample PowerApps application and add a gallery. Assign the data source to the gallery.
Step 4: Assigning the “MediumSize” to the image will not shows up the image in PowerApp. So add the below code in the image source to specify the Base64.
“data:image/jpeg;base64,” & ThisItem.MediumSize