Like
B. Diddy said, some android devices can only hold one item at a time, and even if they don't, clipboard items are gradually overwritten as you copy more items to it. The only way I've ever got an image copied to the clipboard is from taking a screenshot. Your screenshots should be in one of the following paths:
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sdcard/Pictures/Screenshots
mnt/sdcard/Pictures/Screenshots
storage/emulated/0/Pictures/Screenshots
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This will vary on your device and which file explorer you are using. The above paths are the
whole paths, but your stock file explorer starts from these locatoins in the same order as before:
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sdcard/
sdcard/
0/
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So you should only have to look for the Screenshots folder under Pictures. Hope this helps.