Composer says it has found the package put your project requires a higher stability:
The package is not available in a stable-enough version according to your minimum-stability....
To resolve the issue set the minimum stability to dev for that one package in your project's composer.json.
"wjb/image-bundle": "*@dev"
Read more on stability flags here.
You can also set minimum stability in your composer.json for your whole project to one of dev,alpha,beta,rc or stable. But as this will affect your whole project this is not recommended.
// ...
"require" : {
// ... dependencies here
},
"minimum-stability" : "dev",
// ...