You can get the old ImageCompose behavior by using Overlay instead:

Overlay[{i1, i2}] 

Edit:

As pointed out by the comment by ybeltukov the Head of an Overlay is "Overlay" and therefore doesn't match the Head of ImageCompose, which is "Image". I didn't realize this, because exporting to a .png file did handle the transformation.
One can use e.g.

ImportString@ExportString[Overlay[{i1, i2}], "PNG"] 

to get an object with Head "Image", and that therefore can be used the same way as an object created with ImageCompose inside the notebook.

You can get the old ImageCompose behavior by using Overlay instead:

Overlay[{i1, i2}] 

Edit:

As pointed out by the comment by ybeltukov the Head of an Overlay is "Overlay" and therefore doesn't match the Head of ImageCompose, which is "Image". I didn't realize this, because exporting to a .png file did handle the transformation.
One can use e.g.

ImportString@ExportString[Overlay[{i1, i2}], "PNG"] 

to get an object with Head "Image", and that therefore can be used the same way as an object created with ImageCompose inside the notebook.

You can get the old ImageCompose behavior by using Overlay instead:

Overlay[{i1, i2}] 

You can get the old ImageCompose behavior by using Overlay instead:

Overlay[{i1, i2}] 

Edit:

As pointed out by the comment by ybeltukov the Head of an Overlay is "Overlay" and therefore doesn't match the Head of ImageCompose, which is "Image". I didn't realize this, because exporting to a .png file did handle the transformation.
One can use e.g.

ImportString@ExportString[Overlay[{i1, i2}], "PNG"] 

to get an object with Head "Image", and that therefore can be used the same way as an object created with ImageCompose inside the notebook.