When i see fallen wood around here I'm suspect of it especially if it lies beneath the tree and not put aside away from the tree in a pile. It doesnt mean it isnt good wood as storms move in and take good wood down.
I look at the end of the branch where it got severed. If the end looks like it would if you took a piece of wet sapling and snapped it in half chances are its good wood. Sometimes wood found will have been sawed and that usually is an indicator of perhaps pruning was done on a tree and the wood should be good.
Bad wood where it came off the tree usually has a look about it, the end looks soft and rotten. Ive sawn the ends of rotten wood branches off flat and you can see sawdust within.
Anyhow, what i usually end up doing to test a piece is give it a flex test if rotten it wont take much to snap it. Hope this helps you a bit.
That wood you have pictured from what i can tell looks pretty good.
I look at the end of the branch where it got severed. If the end looks like it would if you took a piece of wet sapling and snapped it in half chances are its good wood. Sometimes wood found will have been sawed and that usually is an indicator of perhaps pruning was done on a tree and the wood should be good.
Bad wood where it came off the tree usually has a look about it, the end looks soft and rotten. Ive sawn the ends of rotten wood branches off flat and you can see sawdust within.
Anyhow, what i usually end up doing to test a piece is give it a flex test if rotten it wont take much to snap it. Hope this helps you a bit.
That wood you have pictured from what i can tell looks pretty good.