God’s claim to have created humans in His image was just a figure of speech.
It is generally considered in Christianity that "in his image" means self aware. Self identifying in relation to existence and capable of abstract thought beyond ones identified self if that's what you meant by figure of speech.
don’t you think that there is a possible human being, or any not God being, that does not need any supervision in order to perform what is best for it?
Not if that being is in some fashion not omniscient. Omniscience is required in order to factor in universal relations to what actions that being might take making it possible to conclude what's best for it.
Like in chess...and this is horribly simplistic. One might see an opportunity to take the Queen. The most powerful piece on the board. One's decision to take the Queen would be based upon ones ability to project into ones reasoning all the subsequent possible moves effected by and effecting the results of taking that Queen. Lets say your projection of the possible 10 future moves indicates to you that taking the Queen is the best move. However the eleventh move places you in a position firmly on the road to being checkmated because of your initially taking that Queen. Of course we must consider the nature of the phrase "best for". It may very well be that you've decided that its best for you to be checkmated. However that decision too would be based upon a finite understanding of your being and purpose barring omniscience.
or that it realises, out of simple logic, that disobeying an omniscient almighty being is highly irrational?
Again your realization would be based upon limited understanding and while it may be realistic to believe so your limitations would also make it realistic to think yourself out of that.
Honestly, I have no problem to imagine such a being. And as long as such a being belongs to a possible state of affairs of the world, the label “perfect” applied to Adam and Eve does not obtain..
Its one thing to have no problem imagining such a being. Its another to confirm its possibility.
Also you've not defined the relationship such a being has with regards to Adam and Eve's perfection.
Are you saying that a perfect human being should be one which knows perfectly what is best for it to do?
Consider...do you think Adam or Eve had a conception of what it meant to lie? To deceive or be deceived? To actually know what it meant to trust one thing over another?