Open pictures with a double click

A double click on a picture in Explorer opens it in the app Windows has for it. Windows lets only you choose that app — no app can make itself the one — so here is where, in a minute.

From the viewer: one click to the right place

The first time a picture opens in Cobalt Photo's viewer, a small note at the top asks: Open pictures here with a double click? Choose in Windows… opens Windows' page for Cobalt Photo Viewer at once; Not now closes the note, and it does not come back.

The same button is in ⋯ → Tools → Options… → Viewer → Open pictures with a double click, for any time later.

In Windows' settings

1. On Windows' page for Cobalt Photo Viewer (the button above takes you there; otherwise Settings → Apps → Default apps, then Cobalt Photo Viewer in the list).
2. If Windows shows Set default at the top, click it: every picture type the viewer opens is its own at once.
3. Otherwise click the types you want one by one — .jpg, .png, .heic, .webp… — and choose Cobalt Photo Viewer for each.

For one type, from Explorer

Right-click a picture of that type, choose Open with → Choose another app, pick Cobalt Photo Viewer and click Always. Pictures of that type open in it from then on.

Going back

To have another app open your pictures again, do the same with that app: Windows keeps one app for each type, the last one you chose.